Public Vulnerability Reports

Multiple Vendor X Server Record and Security Extensions Multiple Memory Corruption Vulnerabilities

06.11.08

BACKGROUND

The X Window System is a graphical windowing system based on a client/server model. 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 multiple memory corruption vulnerabilities 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.

Multiple vulnerabilities are present in the Record and Security extensions. In both cases, untrusted values are taken from a client request, and used to swap the byte order of heap memory that follows the client request. Since the number of bytes to swap is not properly validated, it is possible to corrupt heap memory located after the request. The following functions contain vulnerable code:

 SProcSecurityGenerateAuthorization() SProcRecordCreateContext() SProcRecordRegisterClients() 

ANALYSIS

Exploitation allows an attacker to execute arbitrary code with the privileges of the X server, typically root. In order to exploit these vulnerabilities, 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 these vulnerabilities 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 in the SECURITY extension can be prevented by preventing the X server from loading the extension. However, doing so may seriously impair the functionality of the server. Adding the following lines to the X configuration file will disable the SECURITY extension:

 Section "Extensions" Option "SECURITY" "disable" EndSection 

VENDOR RESPONSE

The X.Org team has addressed these vulnerabilities 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-2008-1377 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.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

Free tools, research and upcoming events
http://labs.idefense.com/

LEGAL NOTICES

Copyright © 2008 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.