The imagegammacorrect function in ext/gd/gd.c in PHP before 5.6.25 and 7.x before 7.0.10 does not properly validate gamma values, which allows remote attackers to cause a denial of service (out-of-bounds write) or possibly have unspecified other impact by providing different signs for the second and third arguments.
openwall.com/lists/oss-security/2016/09/02/9
rhn.redhat.com/errata/RHSA-2016-2750.html
www.php.net/ChangeLog-5.php
www.php.net/ChangeLog-7.php
www.securityfocus.com/bid/92757
www.securitytracker.com/id/1036680
bugs.php.net/bug.php?id=72730
github.com/php/php-src/commit/1bd103df00f49cf4d4ade2cfe3f456ac058a4eae?w=1
security.gentoo.org/glsa/201611-22
www.tenable.com/security/tns-2016-19