Messages in Apple iOS before 9.3, OS X before 10.11.4, and watchOS before 2.2 does not properly implement a cryptographic protection mechanism, which allows remote attackers to read message attachments via vectors related to duplicate messages.
lists.apple.com/archives/security-announce/2016/Mar/msg00000.html
lists.apple.com/archives/security-announce/2016/Mar/msg00001.html
lists.apple.com/archives/security-announce/2016/Mar/msg00004.html
www.securitytracker.com/id/1035353
support.apple.com/HT206166
support.apple.com/HT206167
support.apple.com/HT206168