GNOME Display Manager (gdm) before 2.21.1 allows local users to change permissions of arbitrary directories via a symlink attack on /tmp/.X11-unix/.

The remote Oracle Linux 5 host has packages installed that are affected by a vulnerability as referenced in the ELSA-2013-1213 advisory.

    - Don't try to pre-create directories that are internal       implementation details of X.
      Resolves: #997619 CVE-2013-4169

    initscripts
    - create /tmp/.X11-unix in rc.sysinit (#997622, CVE-2013-4169)

Tenable has extracted the preceding description block directly from the Oracle Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

A race condition was found in the way GDM handled the X server sockets directory located in the system temporary directory. An unprivileged user could use this flaw to perform a symbolic link attack, giving them write access to any file, allowing them to escalate their privileges to root. (CVE-2013-4169)

Note that this erratum includes an updated initscripts package. To fix CVE-2013-4169, the vulnerable code was removed from GDM and the initscripts package was modified to create the affected directory safely during the system boot process. Therefore, this update will appear on all systems, however systems without GDM installed are not affected by this flaw.

The system must be rebooted for this update to take effect.

Updated gdm and initscripts packages that fix one security issue are now available for Red Hat Enterprise Linux 5.

The Red Hat Security Response Team has rated this update as having important security impact. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available from the CVE link in the References section.

The GNOME Display Manager (GDM) provides the graphical login screen, shown shortly after boot up, log out, and when user-switching.

A race condition was found in the way GDM handled the X server sockets directory located in the system temporary directory. An unprivileged user could use this flaw to perform a symbolic link attack, giving them write access to any file, allowing them to escalate their privileges to root. (CVE-2013-4169)

Note that this erratum includes an updated initscripts package. To fix CVE-2013-4169, the vulnerable code was removed from GDM and the initscripts package was modified to create the affected directory safely during the system boot process. Therefore, this update will appear on all systems, however systems without GDM installed are not affected by this flaw.

Red Hat would like to thank the researcher with the nickname vladz for reporting this issue.

All users should upgrade to these updated packages, which correct this issue. The system must be rebooted for this update to take effect.

ID	Name	Product	Family	Severity
69806	Oracle Linux 5 : gdm (ELSA-2013-1213)	Nessus	Oracle Linux Local Security Checks	high
69796	Scientific Linux Security Update : gdm on SL5.x i386/srpm/x86_64 (20130905)	Nessus	Scientific Linux Local Security Checks	medium
69795	RHEL 5 : gdm (RHSA-2013:1213)	Nessus	Red Hat Local Security Checks	medium
69791	CentOS 5 : gdm / initscripts (CESA-2013:1213)	Nessus	CentOS Local Security Checks	medium

Detections

Analytics

CVE-2013-4169

high

Tenable Plugins

high

medium

medium

medium