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Polytechnic University ISIS Security Advisory            PUISIS10212005
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                                                  http://isis.poly.edu/
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~ Application: Electric Sheep v2.6.3
~    Severity: Medium-High
~       Title: Multiple Network-related Vulnerabilities in Electric Sheep
~        Date: October 20, 2005
~          ID: PUISIS10212005
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Summary
========
The lack of an authentication framework for downloaded sheep mpegs, as
well as its dependence on and vulnerabilities in cURL allows an
attacker to send and display arbitrary movie files in the Electric
Sheep client and perform arbitrary local and remote code execution.

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
===========
By spoofing the DNS entry for sheepserver.net or otherwise redirecting
the Electric Sheep client to a malicious sheep server, it is possible
to force the Electric Sheep client to download and display arbitrary
mpegs due to a lack of authentication of the sheep server and sheep
mpegs. At minimum, a rogue sheep server would need to respond to the
Electric Sheep client with list.gz, a list of sheep available for
download, and the referenced mpegs. To properly display the mpegs, they
need to contain special footer information which can be found at the
bottom of any pre-existing Electric Sheep mpegs.

Electric sheep uses cURL internally for interaction with the Electric
Sheep server. Two recent vulnerabilities in cURL can be exploited
through malicious interaction with the Electric Sheep client.

As in the previous vulnerability, spoofing the DNS entry of
sheepserver.net or otherwise redirecting the Electric Sheep client
to a malicious sheep server and replacing it with an appropriate HTTP
30x response can allow remote code execution through cURL due to an
NTLM buffer overflow vulnerability [1,2].

Calling the Electric Sheep client by command line, configuration file,
or otherwise with a malicious sheep server URL allows local code
execution through cURL due to a URL buffer overflow vulnerability.
In addition, by redirecting the Electric Sheep client to a rogue sheep
server and supplying a list of maliciously formatted URLs it is
possible to exploit the same cURL URL buffer overflow vulnerability
remotely. This is possible because the Electric Sheep client makes
direct system calls to the vulnerable cURL application from network
supplied input [3,4].

Impact
======
Spoofing the DNS entry for sheepserver.net or otherwise redirecting
the Electric Sheep client to a rogue sheep server, it is possible to
remotely control the video displayed or remotely execute code on all
Electric Sheep clients affected by such a redirection. Local code
execution is also possible due to a cURL vulnerability.

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.

References
==========

  [ 1 ] libcurl NTLM Buffer Overflow Vulnerability
        http://curl.haxx.se/docs/adv_20051013.html

  [ 2 ] CVE-2005-3185
        http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-3185

  [ 3 ] libcurl URL Buffer Overflow Vulnerability
        http://curl.haxx.se/docs/adv_20051207.html

  [ 4 ] CVE-2005-4077
        http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-4077

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.

These vulnerabilities were 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
=======
Daniel Guido dguido@gmail.com
Michael Aiello http://www.michaelaiello.com/