This indicates an attack attempt to exploit a Denial of Service vulnerability in PHP.
The vulnerability is a result of the application's failure to sanitize HTTP requests with crafted data. As a result, a remote attack may be able to exploit this to cause a denial of service condition on the affected system.
PHP before 5.4.41
PHP 5.5.x before 5.5.25
PHP 5.6.x before 5.6.9
Denial of Service: Remote attackers can crash vulnerable systems.
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