zlib in the Compression component in Apple iOS before 9.2, OS X before 10.11.2, tvOS before 9.1, and watchOS before 2.1 does not initialize memory for an unspecified data structure, which allows remote attackers to execute arbitrary code via a crafted web site.
http://lists.apple.com/archives/security-announce/2015/Dec/msg00000.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00001.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00002.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00005.html
http://www.securityfocus.com/bid/78719
http://www.securitytracker.com/id/1034344
https://support.apple.com/HT205635
https://support.apple.com/HT205637