This indicates an attack attempt to exploit an Insecure Deserialization Vulnerability in Oracle WebLogic Server.
A remote attacker could exploit this vulnerability by encrypting a crafted serialized object and sending it in a crafted T3 message to the target server. Successful exploitation can result in result in arbitrary code execution under the security context of the affected server.
Oracle WebLogic Server 10.3.6
Oracle WebLogic Server 12.1.3
Oracle WebLogic Server 188.8.131.52
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.