cmd.exe Unicode Buffer Overflow (SEH)


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# Exploit Title: cmd.exe Unicode Buffer Overflow (SEH)
# Date: 7/8/2010
# Author: bitform
# Software Link: N/A
# Version: N/A
# Tested on: Windows Server 2003 SP2 and Windows XP SP2
# CVE : none

1) Acknowledgements

Props to Dan Crowley (@dan_crowley) at Core Security Technologies
for doing the research on Windows File Pseudonyms and coming up
with the idea for this buffer overflow.

His presentation can be found here:

2) Bug

The TYPE command in Windows is equivalent to cat in *nix. It simply
outputs the contents of a file to stdout. If you use TYPE in conjunction
with the device file CON, you can feed stdin into a file.

Example: TYPE CON > evil.txt

CON is also interpreted as a file so you can append an extension to
it. Supplying a overly large extension will overflow the structured
exception handler.

This buffer overflow is not exploitable since cmd.exe and it's DLLs
are all compiled with SafeSEH. Oh well. :#D

3) Code

Note: The two B's is where the SEH is overwritten.