X.Org Xserver before 1.4.1 allows local users to determine the existence of arbitrary files via a filename argument in the -sp option to the X program, which produces different error messages depending on whether the filename exists.
Fedora Core - Arbitrary File Permission Change via Symlink Attack on /tmp/.font-unix
The init.d script for the X.Org X11 xfs font server on various Linux distributions might allow local users to change the permissions of arbitrary files via a symlink attack on the /tmp/.font-unix temporary file.