Red Hat Linux Advisory: GDM

Red Hat Security Advisory

1. Topic:

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.

2. Relevant releases/architectures:

Red Hat Linux 7.1 – i386
Red Hat Linux 7.1 for iSeries (64 bit) – ppc
Red Hat Linux 7.1 for pSeries (64 bit) – ppc
Red Hat Linux 7.2 – i386, ia64
Red Hat Linux 7.3 – i386
Red Hat Linux 8.0 – i386
Red Hat Linux 9 – i386

3. Problem description:

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.

4. Solution:

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.

5. RPMs required:

Red Hat Linux 7.1:

SRPMS:
ftp://updates.redhat.com/7.1/en/os/SRPMS/gdm-2.0beta2-46.src.rpm

i386:
ftp://updates.redhat.com/7.1/en/os/i386/gdm-2.0beta2-46.i386.rpm

Red Hat Linux 7.1 for iSeries (64 bit):

SRPMS:

ftp://updates.redhat.com/7.1/en/os/iSeries/SRPMS/gdm-2.0beta2-46.src.rpm

ppc:

ftp://updates.redhat.com/7.1/en/os/iSeries/ppc/gdm-2.0beta2-46.ppc.rpm

Red Hat Linux 7.1 for pSeries (64 bit):

SRPMS:

ftp://updates.redhat.com/7.1/en/os/pSeries/SRPMS/gdm-2.0beta2-46.src.rpm

ppc:

ftp://updates.redhat.com/7.1/en/os/pSeries/ppc/gdm-2.0beta2-46.ppc.rpm

Red Hat Linux 7.2:

SRPMS:
ftp://updates.redhat.com/7.2/en/os/SRPMS/gdm-2.2.3.1-21.src.rpm

i386:
ftp://updates.redhat.com/7.2/en/os/i386/gdm-2.2.3.1-21.i386.rpm

ia64:
ftp://updates.redhat.com/7.2/en/os/ia64/gdm-2.2.3.1-21.ia64.rpm

Red Hat Linux 7.3:

SRPMS:
ftp://updates.redhat.com/7.3/en/os/SRPMS/gdm-2.2.3.1-23.src.rpm

i386:
ftp://updates.redhat.com/7.3/en/os/i386/gdm-2.2.3.1-23.i386.rpm

Red Hat Linux 8.0:

SRPMS:
ftp://updates.redhat.com/8.0/en/os/SRPMS/gdm-2.4.0.7-14.src.rpm

i386:
ftp://updates.redhat.com/8.0/en/os/i386/gdm-2.4.0.7-14.i386.rpm

Red Hat Linux 9:

SRPMS:
ftp://updates.redhat.com/9/en/os/SRPMS/gdm-2.4.1.3-5.1.src.rpm

i386:
ftp://updates.redhat.com/9/en/os/i386/gdm-2.4.1.3-5.1.i386.rpm

6. Verification:

MD5 sum Package Name

9704d602c1d7101b95ca80f09d115cf4
7.1/en/os/SRPMS/gdm-2.0beta2-46.src.rpm
1badaf70349be1f21e4b4a990835a247
7.1/en/os/i386/gdm-2.0beta2-46.i386.rpm
9704d602c1d7101b95ca80f09d115cf4
7.1/en/os/iSeries/SRPMS/gdm-2.0beta2-46.src.rpm
c4d56f8b41f1a006c575dd7c5fdbad03
7.1/en/os/iSeries/ppc/gdm-2.0beta2-46.ppc.rpm
9704d602c1d7101b95ca80f09d115cf4
7.1/en/os/pSeries/SRPMS/gdm-2.0beta2-46.src.rpm
c4d56f8b41f1a006c575dd7c5fdbad03
7.1/en/os/pSeries/ppc/gdm-2.0beta2-46.ppc.rpm
380aa52d404a7e1a5ad64e94ced8a938
7.2/en/os/SRPMS/gdm-2.2.3.1-21.src.rpm
abeb24df46ba93d175819a9222f86071
7.2/en/os/i386/gdm-2.2.3.1-21.i386.rpm
987175704054c3852c3275d4ce8155c2
7.2/en/os/ia64/gdm-2.2.3.1-21.ia64.rpm
9c6defce518879748d5e335e5ff54d4f
7.3/en/os/SRPMS/gdm-2.2.3.1-23.src.rpm
a8b30c05951f1d88f0f374b84772be16
7.3/en/os/i386/gdm-2.2.3.1-23.i386.rpm
3085c2df6e5215d23f2f0458cccaa578
8.0/en/os/SRPMS/gdm-2.4.0.7-14.src.rpm
22311861baaec59b7c32b3258f6f40b1
8.0/en/os/i386/gdm-2.4.0.7-14.i386.rpm
8df8308fc16b3a2c8fbaf1fd99142274
9/en/os/SRPMS/gdm-2.4.1.3-5.1.src.rpm
64eea2519454422dba6f451573e0c3e3
9/en/os/i386/gdm-2.4.1.3-5.1.i386.rpm

These packages are GPG signed by Red Hat for security. Our key
is available from http://www.redhat.com/security/keys.html

You can verify each package with the following command:

rpm –checksig -v <filename>

If you only wish to verify that each package has not been
corrupted or tampered with, examine only the md5sum with the
following command:

md5sum <filename>

7. References:

http://www.tldp.org/HOWTO/XDMCP-HOWTO/procedure.html#SECURITY

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0547

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0548

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0549

8. Contact:

The Red Hat security contact is <[email protected]>. More
contact details at http://www.redhat.com/solutions/security/news/contact.html

Copyright 2003 Red Hat, Inc.