This indicates an attack attempt to exploit a Memory Corruption vulnerability in PHP.
The vulnerability is due to an error on a function when the vulnerable application is parsing XML strings. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
PHP Group PHP 5.3.x prior to 5.3.27
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.