The make-temp-name Lisp function in Emacs 20 creates temporary files with predictable names, which allows attackers to conduct a symlink attack.

lisp/net/browse-url.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on a /tmp/Mosaic.##### temporary file.

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.

lisp/gnus/gnus-fun.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on the /tmp/gnus.face.ppm temporary file.

lisp/emacs-lisp/find-gc.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on a temporary file under /tmp/esrc/.

Emacs 20 does not properly set permissions for a slave PTY device when starting a new subprocess, which allows local users to read or modify communications between Emacs and the subprocess.

rcs2log, as used in Emacs 20.4, xemacs 21.1.10 and other versions before 21.4, and possibly other packages, allows local users to modify files of other users via a symlink attack on a temporary file.