ext/libxml/libxml.c in PHP before 5.5.22 and 5.6.x before 5.6.6, when PHP-FPM is used, does not isolate each thread from libxml_disable_entity_loader changes in other threads, which allows remote attackers to conduct XML External Entity (XXE) and XML Entity Expansion (XEE) attacks via a crafted XML document, a related issue to CVE-2015-5161.
https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1509817
http://www.ubuntu.com/usn/USN-2952-2
http://www.ubuntu.com/usn/USN-2952-1
http://www.securityfocus.com/bid/87470
http://www.php.net/ChangeLog-5.php
http://www.openwall.com/lists/oss-security/2016/04/24/1
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00056.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00033.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00031.html
http://git.php.net/?p=php-src.git%3Ba=commit%3Bh=de31324c221c1791b26350ba106cc26bad23ace9