OSEC

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Re: [VulnDiscuss] Main thread's exception handler

From: Halvar Flake (HalVargmx.de)
Date: Tue May 18 2004 - 17:04:49 CDT


Hey all,

I have not read the exploit either, but the first threads TEB address
is static, and if you happen to know what you´re doing you can use this
to hijack the top-level pointer to the SEH chain (fs:0 of the first
thread is aliased to 0x7FFDE000 if I recall correctly) reliably -- this
is superior to using the UnhandledExceptionFilter ptr. The technique
is not much fun unless you can do multiple
(read: as many as you wish)
writes, and I would assume it is far inferior to other published approaches.
It is quite aged as well ("vintage exploits" ;), dating to some time around
2001/2002 IIRC.

If you get a decent number of writes, it can be quite useful tho. Does
anyone know more about Windows randomizing TEB/PEB addresses in XPSP2 ?

Cheers,
Halvar

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