This indicates an attack attempt to exploit a Code Execution vulnerability in Oracle WebLogic Server.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the wls9_async component, when handling a maliciously crafted HTTP request. A remote attacker may be able exploit this to execute arbitrary code within the context of the application via a crafted request.
Oracle Weblogic Server 10.X
Oracle Weblogic Server 12.1.3
System Compromise: Remote attackers can gain control of vulnerable systems
Apply patch available from the vendor: