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Gentoo Linux Security Advisory                           GLSA 200402-02
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~                                            http://security.gentoo.org
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~  Severity: High
~     Title: XFree86 Font Information File Buffer Overflow
~      Date: February 11, 2004
~        ID: 200402-02

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Synopsis
========

Exploitation of a buffer overflow in the XFree86 Project Inc.'s XFree86
X Window System allows local attackers to gain root privileges.

Background
==========

XFree86 provides a client/server interface between display hardware
and the desktop environment while also providing both the windowing
infrastructure and a standardized API. XFree86 is platform
independent, network-transparent and extensible.

Description
===========

Exploitation of a buffer overflow in the XFree86 Window System
discovered by iDefence [ 1 ] allows local attackers to gain root privileges.

The problem exists in the parsing of the 'font.alias' file. The X
 server
(running as root) fails to check the length of the user provided input,
so a malicious user may craft a malformed 'font.alias' file causing a
buffer overflow upon parsing, eventually leading to the execution of
arbitrary code.

To reproduce the overflow on the command line, you can run:

# cat > fonts.dir <<EOF
~  1
~  word.bdf \
~  -misc-fixed-medium-r-semicondensed--13-120-75-75-c-60-iso8859-1
~  EOF
# perl -e 'print "0" x 1024 . "A" x 96 . "\n"'
 > fonts.alias
# X :0 -fp $PWD

{Some output removed}... Server aborting... Segmentation fault (core dumped)

Impact
======

Successful exploitation can lead to a root compromise provided
that the attacker is able to execute commands in the X11
subsystem. This can be done either by having console access to the
target or through a remote exploit against any X client program
such as a web-browser, mail-reader or game.

Workaround
==========

No immediate workaround is available; a software upgrade is required.

Gentoo has released XFree 4.2.1-r3, 4.3.0-r4 and 4.3.99.902-r1 and
encourages all users to upgrade their XFree86 installations. Vulnerable
versions are no longer available in Portage.

Resolution
==========

All users are recommended to upgrade their XFree86 installation:

~    # emerge sync
~    # emerge -pv x11-base/xfree
~    # emerge x11-base/xfree

References
==========

[1] www.idefense.com/application/poi/display?id=72&type=vulnerabilities

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at
http://bugs.gentoo.org.

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