Common Vulnerabilities and Exposures assigned an identifier CVE-2013-1056 to the following vulnerability:
X.org X server 1.13.3 and earlier, when not run as root, allows local users to cause a denial of service (crash) or possibly gain privileges via vectors involving cached xkb files.
Not vulnerable. This issue did not affect the versions of xorg-x11-server as shipped with Red Hat Enterprise Linux 5 and 6 as our products did not include the vulnerable patch.
The vulnerability was introduced due to a Ubuntu specific patch, which we never used with the xorg-x11-server we ship with our products.