The Accessibility subsystem in Apple iOS before 8 allows attackers to interfere with screen locking via vectors related to AssistiveTouch events.
https://exchange.xforce.ibmcloud.com/vulnerabilities/96105
http://www.securitytracker.com/id/1030866
http://www.securityfocus.com/bid/69926
http://www.securityfocus.com/bid/69882
http://support.apple.com/kb/HT6441
http://archives.neohapsis.com/archives/bugtraq/2014-09/0106.html