X.org libFS 1.0.4 and earlier allows X servers to trigger allocation of insufficient memory and a buffer overflow via vectors related to an unexpected sign extension in the FSOpenServer function.
http://www.x.org/wiki/Development/Security/Advisory-2013-05-23
http://www.ubuntu.com/usn/USN-1853-1
http://www.securityfocus.com/bid/60130