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X Server TOG-CUP Extension Information Disclosure Vulnerability (200



iDefense Security Advisory 01.17.08: Multiple Vendor X Server TOG-CUP Extension Information Disclosure Vulnerability
iDefense Security Advisory 01.17.08: Multiple Vendor X Server TOG-CUP Extension Information Disclosure Vulnerability



iDefense Security Advisory 01.17.08
http://labs.idefense.com/intelligence/vulnerabilities/ 
Jan 17, 2008

I. BACKGROUND

The X Window System (or X11) is a graphical windowing system used on
Unix-like systems. It is based on a client/server model. More
information about about The X Window system is available at the
following URL.

http://en.wikipedia.org/wiki/X_Window_System 

II. DESCRIPTION

Local exploitation of an information disclosure vulnerability in the
X.Org X server, as included in various vendors' operating system
distributions, could allow an attacker to gain access to sensitive
information stored in server memory.

The vulnerable code exists within the TOG-CUP extension. A 32-bit client
supplied value is taken directly from the request, and then used as an
index into an array. The value located at this index is then stored
into a buffer which is later sent to the client. This allows a client
to read memory from arbitrary locations in server memory.

III. ANALYSIS

Exploitation allows an attacker to read arbitrary memory within the X
Server's address space.

By itself, the impact of this vulnerability is minimal. However, when
coupled with a code execution vulnerability, this vulnerability can be
used to greatly increase the reliability of an exploit.

If an X Server is configured to listen for TCP based client connections,
and a client is granted access to create sessions (via the xhosts file),
then the vulnerability can be exploited remotely.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in X.Org X11
version R7.3. Previous versions may also be affected.

V. WORKAROUND

If the TOG-CUP extension has not been built-in to the server, then it
can be prevented from loading by inserting the following into the X
configuration file (usually in /etc/X11/xorg.conf).

  Section "Module"
    SubSection "extmod"
      Option "omit TOG-CUP"
    EndSubSection
  EndSection

To check if the extension is built-in to the server, grep the output of
the X Server log file as shown below.

  grep built-in /var/log/Xorg.0.log

The result will list all built in extensions. The location of the log
file may need to be changed.

VI. VENDOR RESPONSE

The X.Org team has addressed this vulnerability with the release of
Xserver version 1.4.1. Additionally, patches for versions 1.4 and 1.2
have been made available. For more information, consult the X.Org
advisory at the following URL.

http://lists.freedesktop.org/archives/xorg/2008-January/031918.html 

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-6428 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for 
security problems.

VIII. DISCLOSURE TIMELINE

11/29/2007  Initial vendor notification
12/13/2007  Initial vendor response
01/17/2008  Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to VeriSign iDefense by regenrecht.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php 

Free tools, research and upcoming events
http://labs.idefense.com/ 

X. LEGAL NOTICES

Copyright =A9 2008 iDefense, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please e-mail customerservice@idefense.com for permission. 

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
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