The bcpowmod function in ext/bcmath/bcmath.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 accepts a negative integer for the scale argument, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted call.
https://security.gentoo.org/glsa/201611-22
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05390722
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05320149
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05240731
https://git.php.net/?p=php-src.git%3Ba=commit%3Bh=d650063a0457aec56364e4005a636dc6c401f9cd
http://www.securityfocus.com/bid/90173
http://www.openwall.com/lists/oss-security/2016/05/05/21
http://www.debian.org/security/2016/dsa-3602
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://php.net/ChangeLog-7.php
http://php.net/ChangeLog-5.php
http://lists.opensuse.org/opensuse-updates/2016-06/msg00027.html
http://lists.opensuse.org/opensuse-updates/2016-05/msg00086.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183736.html