This indicates an attack attempt to exploit a Cross-Site Scripting Vulnerability in PHP Group PHP.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker can exploit this to execute arbitrary script code within the context of the user's browser.
PHP Group PHP 7.0.x prior to 7.0.27
PHP Group PHP 7.1.x prior to 7.1.13
PHP Group PHP 7.2.x prior to 7.2.1
PHP Group PHP prior to 5.6.33
System Compromise: Remote attackers can execute arbitrary script code in the context of the affected site.
Apply the most recent upgrade or patch from the vendor: