The Assets component in Apple iOS before 10 allows man-in-the-middle attackers to block software updates via vectors related to lack of an HTTPS session for retrieving updates.
https://support.apple.com/HT207143
http://www.securitytracker.com/id/1036797
http://www.securityfocus.com/bid/92932
http://lists.apple.com/archives/security-announce/2016/Sep/msg00008.html
http://lists.apple.com/archives/security-announce/2016/Sep/msg00002.html