The OCSP client in Apple iOS before 9.1 does not check for certificate expiry, which allows remote attackers to spoof a valid certificate by leveraging access to a revoked certificate.
https://support.apple.com/HT205370
https://euvd.enisa.europa.eu/vulnerability/EUVD-2015-6931
http://www.securitytracker.com/id/1033929
http://www.securityfocus.com/bid/77268
http://lists.apple.com/archives/security-announce/2015/Oct/msg00002.html