The php_wddx_pop_element function in ext/wddx/wddx.c in PHP 7.0.x before 7.0.15 and 7.1.x before 7.1.1 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via an inapplicable class name in a wddxPacket XML document, leading to mishandling in a wddx_deserialize call.
https://github.com/php/php-src/commit/8d2539fa0faf3f63e1d1e7635347c5b9e777d47b
https://bugs.php.net/bug.php?id=73831
https://access.redhat.com/errata/RHSA-2018:1296
http://www.securitytracker.com/id/1037659