From the upstream announcement [1]:

A vulnerability has been found in the X11R6 font server code in the handling of the SetEventMask request in xfs - if an invalid mask is specified, it passes that bad mask to the SendErrToClient() function for returning to the client in the error message. Unfortunately, SendErrToClient() expects a pointer, but was being passed the raw mask value, causing it to use the mask as a pointer, either segfaulting (if that happened to be an invalid pointer), or returning whatever data happened to be accessible in the 4 bytes at the address specified by the mask value.

X11R6 through X11R6.6 appear to be vulnerable. The fix shown below was introduced by XFree86 in their 3.3.3 release as part of the commit for: Prototype/ansification cleanup for Xserver/XIE, xfs, fontlib, mkfontdir, and fix some bugs found along the way (#2103, Thomas Dickey).

X11R6.7 incorporated the XFree86 changes, and thus X11R6.7 and later releases from X.Org are not vulnerable.

[1] http://lists.freedesktop.org/archives/xorg-announce/2012-July/002040.html

Statement:

Not vulnerable. This issue did not affect the versions of xorg-x11-xfs as shipped with Red Hat Enterprise Linux 5. It does not affect Red Hat Enterprise Linux 6 as it no longer uses or provides the XFS font server.

Untrusted search path vulnerability in x11perfcomp in XFree86 x11perf before 1.5.4 allows local users to gain privileges via unspecified Trojan horse code in the current working directory.