Tim Brown discovered a shared memory permissions vulnerability in the Mesa 3D graphics library. Some Mesa X11 drivers use shared-memory XImages to implement back buffers for improved performance, but Mesa creates shared memory regions with permission mode 0777. An attacker can access the shared memory without any specific permissions.
For Debian 7 Wheezy, these problems have been fixed in version 188.8.131.52-1+deb7u3.
We recommend that you upgrade your mesa packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/