iDefense Security Advisory 01.17.08 http://labs.idefense.com/intelligence/vulnerabilities/ Jan 17, 2008 I. BACKGROUND The X Window System (or X11) is a graphical windowing system used on Unix-like systems. It is based on a client/server model. More information about about The X Window system is available at the following URL. http://en.wikipedia.org/wiki/X_Window_System II. DESCRIPTION Local exploitation of an information disclosure vulnerability in the X.Org X server, as included in various vendors' operating system distributions, could allow an attacker to gain access to sensitive information stored in server memory. The vulnerable code exists within the TOG-CUP extension. A 32-bit client supplied value is taken directly from the request, and then used as an index into an array. The value located at this index is then stored into a buffer which is later sent to the client. This allows a client to read memory from arbitrary locations in server memory. III. ANALYSIS Exploitation allows an attacker to read arbitrary memory within the X Server's address space. By itself, the impact of this vulnerability is minimal. However, when coupled with a code execution vulnerability, this vulnerability can be used to greatly increase the reliability of an exploit. 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 the vulnerability can be exploited remotely. IV. DETECTION iDefense has confirmed the existence of this vulnerability in X.Org X11 version R7.3. Previous versions may also be affected. V. WORKAROUND If the TOG-CUP extension has not been built-in to the server, then it can be prevented from loading by inserting the following into the X configuration file (usually in /etc/X11/xorg.conf). Section "Module" SubSection "extmod" Option "omit TOG-CUP" EndSubSection EndSection To check if the extension is built-in to the server, grep the output of the X Server log file as shown below. grep built-in /var/log/Xorg.0.log The result will list all built in extensions. The location of the log file may need to be changed. VI. VENDOR RESPONSE The X.Org team has addressed this vulnerability with the release of Xserver version 1.4.1. Additionally, patches for versions 1.4 and 1.2 have been made available. For more information, consult the X.Org advisory at the following URL. http://lists.freedesktop.org/archives/xorg/2008-January/031918.html VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-6428 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 11/29/2007 Initial vendor notification 12/13/2007 Initial vendor response 01/17/2008 Coordinated public disclosure IX. CREDIT This vulnerability was reported to VeriSign 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/ X. LEGAL NOTICES Copyright © 2008 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@xxxxxxxxxxxx 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.
