The LockServer function in os/utils.c in X.Org xserver before 1.11.2 allows local users to change the permissions of arbitrary files to 444, read those files, and possibly cause a denial of service (removed execution permission) via a symlink attack on a temporary lock file.
The XInput extension in X.Org Xserver before 1.4.1 allows context-dependent attackers to execute arbitrary code via requests related to byte swapping and heap corruption within multiple functions, a different vulnerability than CVE-2007-4990.