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Date: Wed, 11 Jun 2008 16:40:28 -0400
From: iDefense Labs <>
Subject: iDefense Security Advisory 06.11.08: Multiple Vendor X Server Render
 Extension AllocateGlyph() Integer Overflow Vulnerability

iDefense Security Advisory 06.11.08
Jun 11, 2008


The X Window System is a graphical windowing system based on a
client/server model. The Render extension is used to provide
Porter-Duff image compositing for the X server. It is built into many X
servers by default, and loaded as a default module when it is not. For
more information, see the vendor's site found at the following link.


Local exploitation of an integer overflow vulnerability in the X.Org X
server, as included in various vendors' operating system distributions,
could allow an attacker to execute arbitrary code with the privileges of
the X server, typically root.

The vulnerability exists within the AllocateGlyph() function, which is
called from several request handlers in the render extension. This
function takes several values from the request, and multiplies them
together to calculate how much memory to allocate for a heap buffer.
This calculation can overflow, which leads to a heap overflow.


Exploitation allows an attacker to execute arbitrary code with the
privileges of the X server, typically root. To exploit this
vulnerability, an attacker must be able 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 is 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.

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 these vulnerabilities can be exploited remotely.


iDefense has confirmed the existence of this vulnerability in X server
1.4 included with X11R7.3, with all patches as of 03/01/08
applied. Previous versions may also be affected.


Access to the vulnerable code can be prevented by preventing the X
server from loading the Render extension. However, doing so may
seriously impair the functionality of the server. Adding the following
lines to the X configuration file will disable the Render extension:

  Section "Extensions"
    Option "RENDER" "disable"


The X.Org team has addressed this vulnerability by releasing patches for
version 1.4 of the X server. For more information, consult the X.Org
advisory at the following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-2360 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


03/26/2008  Initial vendor notification
03/26/2008  Initial vendor response
06/11/2008  Coordinated public disclosure


This vulnerability was reported to iDefense by regenrecht.

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Copyright © 2008 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
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