XFree86 Font Information File Buffer Overflow

1. Gentoo Linux Security Advisory

Advisory Reference	GLSA 200402-02 / 200402-02
Release Date	February 11, 2004
Latest Revision	February 11, 2004: 01
Impact	high
Exploitable	local

Package	Vulnerable versions	Unaffected versions	Architecture(s)
x11-base/xfree	< 4.3.99.902-r1	= 4.2.1-r3, = 4.3.0-r4, >= 4.3.99.902-r1	All supported architectures

Related bugreports: No related gentoo bugreports

Synopsis

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

2. Impact Information

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 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 one can run:

Code Listing 2.1: Description

# 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.

3. Resolution Information

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:

Code Listing 3.1: Resolution

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

4. References

Page updated February 11, 2004

Summary: This is a Gentoo Linux Security Advisory

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