Using The Egghunter Mixin
From Metasploit Unleashed - Mastering The Framework
The MSF egghunter mixin is a wonderful module which can be of great use in exploit development. If you're not familiar with the concepts of egghunters, read this.
A recent vulnerability in the Audacity Audio Editor presented us with an opportunity to examine this mixin in greater depth. In the next module, we will exploit Audacity and create a Metasploit file format exploit module for it. We will not focus on the exploitation method itself or the theory behind it - but dive right into the practical usage of the Egghunter mixin. Setting up Audacity
- Download and install the vulnerable software on your XP SP2 box:
http://www.offensive-security.com/archive/audacity-win-1.2.6.exe http://www.offensive-security.com/archive/LADSPA_plugins-win-0.4.15.exe
- Download and examine the original POC, taken from : http://www.exploit-db.com/exploits/7634/
Porting the PoC
Let's port this POC to an MSF file format exploit module. We can use an existing module to get a general template. The zinfaudioplayer221_pls.rb exploit provides us with a good start.
Our skeleton exploit should look similar to this. Notice our buffer being generated here:
def exploit
buff = Rex::Text.pattern_create(2000)
print_status("Creating '#{datastore['FILENAME']}' file ...")
file_create(buff)
end
We use Rex::Text.pattern_create(2000) to create a unique string of 2000 bytes in order to be able to track buffer locations in the debugger.
Once we have the POC ported, we generate the exploit file and transfer it to our Windows box. Use the generic/debug_trap payloads to begin with.
msf exploit(audacity) > show options Module options: Name Current Setting Required Description ---- --------------- -------- ----------- FILENAME evil.gro yes The file name. OUTPUTPATH /var/www yes The location of the file. Payload options (generic/debug_trap): Name Current Setting Required Description ---- --------------- -------- ----------- Exploit target: Id Name -- ---- 0 Audacity Universal 1.2 msf exploit(audacity) > exploit [*] Creating 'evil.gro' file ... [*] Generated output file /var/www/evil.gro [*] Exploit completed, but no session was created. msf exploit(audacity) >
We open Audacity, attach a debugger to it and import the MIDI gro file.
We immediately get an exception from Audacity, and the debugger pauses:
A quick look at the SEH chain shows that we have overwritten an exception handler.
We take the exception (shift + F9), and see the following:
