Multiple Vendor X Server Render Extension ProcRenderAddGlyphs 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 links.
 
http://en.wikipedia.org/wiki/X_Window_System
 
II. DESCRIPTION
 
Local exploitation of a memory corruption vulnerability in the
"ProcRenderAddGlyphs" 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 Render extension.
Insufficient input validation exists when allocating memory for glyph
management data structures. By sending a specially crafted X protocol
request to the Render 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 Render extension is
not built into the X binary. This can be accomplished by removing the entry
for the Render 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 "render"
 
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-2006-6101 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.
 
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.
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.
 
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