The XSS auditor in WebKit, as used in Apple iOS before 9.3 and Safari before 9.1, does not properly handle redirects in block mode, which allows remote attackers to obtain sensitive information via a crafted URL.
https://support.apple.com/HT206171
https://support.apple.com/HT206166
http://www.securitytracker.com/id/1036344
http://www.securityfocus.com/bid/91358
http://lists.apple.com/archives/security-announce/2016/Mar/msg00005.html
http://lists.apple.com/archives/security-announce/2016/Mar/msg00000.html