Multiple Vendor X Server DBE Extension ProcDbeSwapBuffers Memory
Corruption Vulnerability

iDefense Security Advisory 01.09.07
http://labs.idefense.com/intelligence/vulnerabilities/
Jan 09, 2007

I. BACKGROUND

The X Window System is a graphical windowing system based on a
client/server model. More information about about The X Window system is
available at the following link:

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

II. DESCRIPTION

Local exploitation of a memory corruption vulnerability in the
"ProcDbeSwapBuffers" function in the X.Org and XFree86 X server could
allow an attacker to execute arbitrary code with privileges of the X
server, typically root.

This vulnerability specifically lies within the DBE extension.
Insufficient input validation exists when allocating memory for data
structures. By sending a specially crafted X protocol request to the DBE
extension, an attacker can cause an exploitable memory corruption
condition.

III. ANALYSIS

Successful exploitation allows an attacker to execute arbitrary as the root
user. In order to exploit this vulnerability an attacker would require the
ability to send commands to an affected X server. This typically requires
access to the console, or access to the same account as a user who is on
the console. One method of gaining the required access would be to
remotely exploit a vulnerability in, for example, a graphical web browser.
This would then allow an attacker to exploit this vulnerability and elevate
their privileges to root.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in the X.Org
server version 7.1-1.1.0. Previous versions may also be affected.

V. WORKAROUND

Access to the vulnerable code can be prevented when the DBE extension is
not built into the X binary. This can be accomplished by removing the
entry for the DBE extension from your X server's configuration file, often
stored in /etc/X11 and named xorg.conf or XF86Config-4. To do this, remove
the following line from the 'Module' section:

Load "DBE"

This will prevent the render extension from loading, which may affect the
appearance or operation of some applications.

VI. VENDOR RESPONSE

The X.Org foundation has addressed this vulnerability within version 7.2
RC3 of X.Org's X server. Additionally, patches have been made available
for older releases.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-6103 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

12/04/2006  Initial vendor notification
12/05/2006  Initial vendor response
01/09/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2006 iDefense, Inc.

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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.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on, this
information.