[ GLSA 200402-02 ] XFree86 Font Information File Buffer Overflow

[Tim Yamin <plasmaroo () gentoo org>]

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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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