IOKit SCSI in Apple iOS before 9.2, OS X before 10.11.2, tvOS before 9.1, and watchOS before 2.1 allows attackers to execute arbitrary code in a privileged context or cause a denial of service (NULL pointer dereference) via an app that provides an unspecified userclient type.
https://support.apple.com/HT205641
https://support.apple.com/HT205640
https://support.apple.com/HT205637
https://support.apple.com/HT205635
http://www.securitytracker.com/id/1034344
http://www.securityfocus.com/bid/78719
http://lists.apple.com/archives/security-announce/2015/Dec/msg00005.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00002.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00001.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00000.html