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Multiple Vendor X Server DBE Extension ProcDbeGetVisualInfo Memory Corruption Vulnerability

01.09.07

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

DESCRIPTION

Local exploitation of a memory corruption vulnerability in the "ProcDbeGetVisualInfo" 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.

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.

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.

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.

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.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2006-6102 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

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

CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

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LEGAL NOTICES

Copyright © 2006 Verisign, 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 customer service 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.