iDefense Security Advisory 01.17.08: Multiple Vendor X Server XFree86-Misc Extension Invalid Array Index Vulnerability
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 invalid array index 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 XFree86-Misc extension. When
processing a request, a 32-bit value from the client's request is used
as an index into an array of structures. This structure contains an
array of function pointers, one of which is used later in the request
handling. By supplying a large array index, an arbitrary function
pointer can be dereferenced. This results in the execution of arbitrary
code.
III. ANALYSIS
Exploitation allows an attacker to execute arbitrary code with root
privileges. In order 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.
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 XFree86-Misc 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 XFree86-Misc"
EndSubSection
EndSection
To check if the extension is built-in to the server, grep the output of
the X Server log file.
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-2007-5760 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 response
11/30/2007 Initial vendor notification
01/17/2008 Coordinated public disclosure
IX. CREDIT
This vulnerability was reported to VeriSign iDefense by regenrecht.
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X. LEGAL NOTICES
Copyright © 2008 iDefense, Inc.
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at the time of publishing based on currently available information. Use
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