sys/openbsd/stackprotector.c in libc in Apple iOS 6.1.3 and Mac OS X 10.8.x does not properly parse the Apple strings employed in the user-space stack-cookie implementation, which allows local users to bypass cookie randomization by executing a program with a call-path beginning with the stack-guard= substring, as demonstrated by an iOS untethering attack or an attack against a setuid Mac OS X program.