Ilja van Sprundel of IOActive discovered several security issues in the X.org X server, which may lead to privilege escalation or denial of service.
For the stable distribution (wheezy), these problems have been fixed in version 1.12.4-6+deb7u5.
For the upcoming stable distribution (jessie), these problems will be fixed soon.
For the unstable distribution (sid), these problems have been fixed in version 2:188.8.131.521-1.
We recommend that you upgrade your xorg-server packages.