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.