This indicates an attack attempt to exploit a Denial of Service vulnerability in PHP.
The vulnerability is due to an error in creating a dateInterval object when vulnerable module handles a malicious request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
PHP Group PHP prior to 5.5.6
Denial of Service: Remote attackers can crash vulnerable systems or services
Apply the most recent upgrade or patch from the vendor.