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://www.securitytracker.com/id?1026774
http://support.apple.com/kb/HT5501
http://secunia.com/advisories/48288
http://lists.apple.com/archives/security-announce/2012/Sep/msg00004.html
http://lists.apple.com/archives/security-announce/2012/Mar/msg00001.html