This indicates an attack attempt to exploit a Code Execution Vulnerability in Apache Struts.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
Apache Struts before 18.104.22.168
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the latest update from the vendor.