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 X.org 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" EndSection
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 (http://cve.mitre.org/), 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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