The WiFi Connectivity feature in Apple iOS before 8.4 allows remote Wi-Fi access points to trigger an automatic association, with an arbitrary security type, by operating with a recognized ESSID within an 802.11 network's coverage area.
http://www.securitytracker.com/id/1032761
http://www.securityfocus.com/bid/75490
http://support.apple.com/kb/HT204941
http://lists.apple.com/archives/security-announce/2015/Jun/msg00001.html