Apple iOS before 8.1.1 does not properly enforce the failed-passcode limit, which makes it easier for physically proximate attackers to bypass the lock-screen protection mechanism via a series of guesses.
https://support.apple.com/en-us/HT6590
https://support.apple.com/en-us/HT204418
https://exchange.xforce.ibmcloud.com/vulnerabilities/98776
http://www.securitytracker.com/id/1031232
http://www.securityfocus.com/bid/71138
http://secunia.com/advisories/62504
http://lists.apple.com/archives/security-announce/2014/Nov/msg00000.html