OSEC

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Subject: Re: another Xlib buffer overflow
From: Robert van der Meulen (rvdmCISTRON.NL)
Date: Fri Oct 13 2000 - 21:03:13 CDT


Quoting Michal Zalewski (lcamtufdione.ids.pl):
> On Sat, 14 Oct 2000, Robert van der Meulen wrote:
> > ii xserver-svga 3.3.6-10 X server for SVGA graphics cards
> > <rvdmcrypt:~> export DISPLAY=`perl -e '{print "0" x 128}'`
> Couldn't see ':' there.
It's late at night, and i'm stupid ;)

I've been looking a bit further into this. This actually _does_ trigger
segfaults on both woody and potato.
The problem is, that the display number can only contain numeric values
(Xlib does check _that_). This seriously limits possibilities for inserting
shellcode. With only the hexvalues of '0' to '9' an actual shellcode isn't
possible, but jumping to different addresses is possible.

Greets,
        Robert van der Meulen / Emphyrio

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