Quartz Composer in Apple Mac OS X before 10.7.4, when the RSS Visualizer screensaver is enabled, allows physically proximate attackers to bypass screen locking and launch a Safari process via unspecified vectors.
http://www.securityfocus.com/bid/53473
http://www.securityfocus.com/bid/53445
http://support.apple.com/kb/HT5281
http://lists.apple.com/archives/security-announce/2012/May/msg00001.html