Passcode Lock in Apple iOS before 7.0.2 on iPhone devices allows physically proximate attackers to bypass an intended passcode requirement, and dial arbitrary telephone numbers, by making a series of taps of the emergency-call button to trigger a NULL pointer dereference.
http://support.apple.com/kb/HT5957
http://lists.apple.com/archives/security-announce/2013/Sep/msg00009.html