Public Vulnerability Reports

Multiple Vendor X Server Render Extension Gradient Creation Integer Overflow Vulnerability

11.06.08

BACKGROUND

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.

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

DESCRIPTION

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 occurs when parsing a client request for one of the following functions:

 SProcRenderCreateLinearGradient SProcRenderCreateRadialGradient SProcRenderCreateConicalGradient 

In each case, values are taken from the client request and used to calculate the number of bytes to swap in the client request data. The calculations attempt to verify that the byte swap range if valid, but they are incorrect, which can lead to heap memory being corrupted.

ANALYSIS

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.

DETECTION

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

WORKAROUND

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" EndSection 

VENDOR RESPONSE

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.

http://lists.freedesktop.org/archives/xorg/2008-June/036026.html

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-2362 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

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

CREDIT

This vulnerability was reported to iDefense by regenrecht.

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LEGAL NOTICES

Copyright © 2008 Verisign, Inc.

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