The SoapClient::__call method in ext/soap/soap.c in PHP before 5.4.39, 5.5.x before 5.5.23, and 5.6.x before 5.6.7 does not verify that __default_headers is an array, which allows remote attackers to execute arbitrary code by providing crafted serialized data with an unexpected data type, related to a "type confusion" issue.
https://support.apple.com/kb/HT205031
https://security.gentoo.org/glsa/201606-10
http://www.securitytracker.com/id/1032459
http://www.securityfocus.com/bid/73357
http://www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
http://rhn.redhat.com/errata/RHSA-2015-1218.html
http://rhn.redhat.com/errata/RHSA-2015-1135.html
http://rhn.redhat.com/errata/RHSA-2015-1066.html
http://rhn.redhat.com/errata/RHSA-2015-1053.html
http://php.net/ChangeLog-5.php
http://lists.opensuse.org/opensuse-security-announce/2015-05/msg00005.html
http://lists.apple.com/archives/security-announce/2015/Aug/msg00001.html