dyld in Apple iOS before 9.2, tvOS before 9.1, and watchOS before 2.1 mishandles segment validation, which allows attackers to execute arbitrary code in a privileged context via a crafted app.
lists.apple.com/archives/security-announce/2015/Dec/msg00000.html
lists.apple.com/archives/security-announce/2015/Dec/msg00001.html
lists.apple.com/archives/security-announce/2015/Dec/msg00002.html
www.securitytracker.com/id/1034348
support.apple.com/HT205635
support.apple.com/HT205640
support.apple.com/HT205641