ext/standard/var_unserializer.c in PHP before 5.6.25 and 7.x before 7.0.10 mishandles certain invalid objects, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted serialized data that leads to a (1) __destruct call or (2) magic method call.
https://www.tenable.com/security/tns-2016-19
https://security.gentoo.org/glsa/201611-22
https://github.com/php/php-src/commit/20ce2fe8e3c211a42fee05a461a5881be9a8790e?w=1
http://www.securitytracker.com/id/1036680
http://www.securityfocus.com/bid/92756
http://www.php.net/ChangeLog-7.php
http://www.php.net/ChangeLog-5.php