ext/spl/spl_array.c in PHP before 5.6.26 and 7.x before 7.0.11 proceeds with SplArray unserialization without validating a return value and data type, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted serialized data.
https://www.tenable.com/security/tns-2016-19
https://security.gentoo.org/glsa/201611-22
https://github.com/php/php-src/commit/ecb7f58a069be0dec4a6131b6351a761f808f22e?w=1
https://access.redhat.com/errata/RHSA-2018:1296
http://www.securitytracker.com/id/1036836
http://www.securityfocus.com/bid/93007
http://www.php.net/ChangeLog-7.php