The IOUSBDeviceFamily driver in the USB implementation in the kernel in Apple iOS before 6.1.3 and Apple TV before 5.2.1 accesses pipe object pointers that originated in userspace, which allows local users to gain privileges via crafted code.
http://support.apple.com/kb/HT5704
http://support.apple.com/kb/HT5702
http://lists.apple.com/archives/security-announce/2013/Mar/msg00005.html
http://lists.apple.com/archives/security-announce/2013/Mar/msg00004.html