The idle stream handling in nghttp2 before 1.6.0 allows attackers to have unspecified impact via unknown vectors, aka a heap-use-after-free bug.
https://support.apple.com/HT206169
https://support.apple.com/HT206168
https://support.apple.com/HT206167
https://support.apple.com/HT206166
https://security.gentoo.org/glsa/201612-06
https://nghttp2.org/blog/2015/12/23/nghttp2-v1-6-0/
http://www.securitytracker.com/id/1035353
http://www.openwall.com/lists/oss-security/2015/12/23/6
http://www.openwall.com/lists/oss-security/2015/12/23/10
http://lists.fedoraproject.org/pipermail/package-announce/2016-January/175423.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-January/175085.html
http://lists.apple.com/archives/security-announce/2016/Mar/msg00004.html
http://lists.apple.com/archives/security-announce/2016/Mar/msg00002.html
http://lists.apple.com/archives/security-announce/2016/Mar/msg00001.html
http://lists.apple.com/archives/security-announce/2016/Mar/msg00000.html