WebKit in Apple iOS before 9.3 and Safari before 9.1 mishandles attachment URLs, which makes it easier for remote web servers to track users via unspecified vectors.
https://support.apple.com/HT205639
https://support.apple.com/HT205635
http://www.securitytracker.com/id/1035353
http://www.securityfocus.com/archive/1/537948/100/0/threaded
http://lists.apple.com/archives/security-announce/2015/Dec/msg00003.html
http://lists.apple.com/archives/security-announce/2015/Dec/msg00000.html