This indicates an attack attempt to exploit a Remote Code Execution Vulnerability in PHP FPM.
The vulnerability is due to insufficient sanitizing of user supplied inputs. A remote attacker may be able to exploit this to execute arbitrary commands within the context of the application, via a crafted HTTP request.
PHP versions 7.1.x below 7.1.33, 7.2.x below 7.2.24 and 7.3.x below 7.3.11
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: