lisp/net/tramp-sh.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on a /tmp/tramp.##### temporary file.
http://www.mandriva.com/security/advisories?name=MDVSA-2015:117
http://openwall.com/lists/oss-security/2014/05/07/7
http://lists.gnu.org/archive/html/emacs-diffs/2014-05/msg00060.html