Emacs 21.2.1 does not prompt or warn the user before executing Lisp code in the local variables section of a text file, which allows user-assisted attackers to execute arbitrary commands, as demonstrated using the mode-name variable.
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.
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.
read-passwd and other Lisp functions in Emacs 20 do not properly clear the history of recently typed keys, which allows an attacker to read unencrypted passwords.