X.org libXt 1.1.3 and earlier does not check the return value of the XGetWindowProperty function, which allows X servers to trigger use of an uninitialized pointer and memory corruption via vectors related to the (1) ReqCleanup, (2) HandleSelectionEvents, (3) ReqTimedOut, (4) HandleNormal, and (5) HandleSelectionReplies functions.
http://www.x.org/wiki/Development/Security/Advisory-2013-05-23
http://www.ubuntu.com/usn/USN-1865-1
http://www.securityfocus.com/bid/60133
http://www.openwall.com/lists/oss-security/2013/05/23/3
http://www.debian.org/security/2013/dsa-2680
http://lists.opensuse.org/opensuse-updates/2013-06/msg00138.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-May/106785.html