Apple Mac OS X before 10.7.5 and 10.8.x before 10.8.2 allows local users to read passwords entered into Login Window (aka LoginWindow) or Screen Saver Unlock by installing an input method that intercepts keystrokes.
http://support.apple.com/kb/HT5501
http://lists.apple.com/archives/security-announce/2012/Sep/msg00004.html