AppleMobileFileIntegrity in Apple iOS before 9.2 and tvOS before 9.1 does not prevent changes to access-control structures, which allows attackers to execute arbitrary code in a privileged context via a crafted app.
http://lists.apple.com/archives/security-announce/2015/Dec/msg00000.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00001.html
http://www.securitytracker.com/id/1034348