xpointer.c in libxml2 before 2.9.5 (as used in Apple iOS before 10, OS X before 10.12, tvOS before 10, and watchOS before 3, and other products) does not forbid namespace nodes in XPointer ranges, which allows remote attackers to execute arbitrary code or cause a denial of service (use-after-free and memory corruption) via a crafted XML document.
https://support.apple.com/HT207170
https://support.apple.com/HT207143
https://support.apple.com/HT207142
https://support.apple.com/HT207141
https://security.gentoo.org/glsa/201701-37
https://git.gnome.org/browse/libxml2/commit/?id=c1d1f7121194036608bf555f08d3062a36fd344b
http://www.securitytracker.com/id/1038623
http://www.securitytracker.com/id/1036858
http://www.securityfocus.com/bid/93054
http://lists.apple.com/archives/security-announce/2016/Sep/msg00011.html
http://lists.apple.com/archives/security-announce/2016/Sep/msg00010.html
http://lists.apple.com/archives/security-announce/2016/Sep/msg00008.html
http://lists.apple.com/archives/security-announce/2016/Sep/msg00006.html