GDM allows local user to read any file.

Updated GDM packages are available which correct a bug allowing local users
to read any text files on the system, and a denial of service issue if
XDMCP is enabled.

GDM is the GNOME Display Manager for X.

Versions of GDM prior to 2.4.1.6 contain a bug where GDM will run as root
when examining the ~/.xsession-errors file when using the "examine session
errors" feature, allowing local users the ability to read any text file
on the system by creating a symlink. The Common Vulnerabilities and
Exposures project (cve.mitre.org) has assigned the name CAN-2003-0547 to
this issue.

Red Hat Linux 8.0 and 9 are vulnerable to this issue. Versions of GDM in
earlier releases did not have the "examine session errors" feature and
therefore are not vulnerable to this issue.

Also addressed by these erratum packages are two problems in the X Display
Manager Control Protocol (XDMCP) which allow a denial of service attack
(DoS) by crashing the gdm daemon. The Common Vulnerabilities and
Exposures project (cve.mitre.org) has assigned the names CAN-2003-0548 and
CAN-2003-0549 to these issues.

This attack is only possible if XDMCP is enabled. XDMCP is not enabled by
default in Red Hat Linux distributions, and as documented XDMCP should only
ever be run on trusted networks.

Users of GDM are advised to upgrade to these erratum packages which disable
the "examine session errors" feature and contain backported security fixes
for the XDMCP issues.

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

To update all RPMs for your particular architecture, run:

rpm -Fvh [filenames]

where [filenames] is a list of the RPMs you wish to upgrade. Only those
RPMs which are currently installed will be updated. Those RPMs which are
not installed but included in the list will not be updated. Note that you
can also use wildcards (*.rpm) if your current directory *only* contains the
desired RPMs.

Please note that this update is also available via Red Hat Network. Many
people find this an easier way to apply updates. To use Red Hat Network,
launch the Red Hat Update Agent with the following command:

up2date

This will start an interactive process that will result in the appropriate
RPMs being upgraded on your system.

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2003-0547
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2003-0548
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2003-0549
http://www.tldp.org/HOWTO/XDMCP-HOWTO/procedure.html#SECURITY

DoS