ext/standard/var_unserializer.re in PHP before 5.6.26 mishandles object-deserialization failures, which allows remote attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact via an unserialize call that references a partially constructed object.
https://security.gentoo.org/glsa/201611-22
https://github.com/php/php-src/commit/6a7cc8ff85827fa9ac715b3a83c2d9147f33cd43?w=1
http://www.securitytracker.com/id/1036836
http://www.securityfocus.com/bid/93009