The Passcode Lock implementation in Apple iOS before 6.1.3 does not properly manage the lock state, which allows physically proximate attackers to bypass an intended passcode requirement by leveraging an error in the emergency-call feature.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-0991
http://support.apple.com/kb/HT5704
http://lists.apple.com/archives/security-announce/2013/Mar/msg00004.html