The kernel in Apple iOS before 6.1 and Apple TV before 5.2 does not properly validate copyin and copyout arguments, which allows local users to bypass intended pointer restrictions and access locations in the first kernel-memory page by specifying a length of less than one page.
http://www.securityfocus.com/bid/57595
http://support.apple.com/kb/HT5643
http://support.apple.com/kb/HT5642
http://lists.apple.com/archives/security-announce/2013/Jan/msg00001.html
http://lists.apple.com/archives/security-announce/2013/Jan/msg00000.html