The kernel in Apple iOS before 5.1 does not properly handle debug system calls, which allows remote attackers to bypass sandbox restrictions and execute arbitrary code via a crafted program.
http://lists.apple.com/archives/security-announce/2012/Mar/msg00001.html
http://lists.apple.com/archives/security-announce/2012/Sep/msg00004.html
http://secunia.com/advisories/48288