This indicates an attack attempt to exploit a Remote Code Execution vulnerability in Apache's Struts 2 web application framework.
The vulnerability is due to an improper interpretation of cookies name. As a result, a remote attacker can send a crafted HTTP request to an affected server allowing the attacker to execute arbitrary Java code and OS commands.
Apache Software Foundation Struts 2 version 188.8.131.52 and earlier versions
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.