This indicates an attack attempt to exploit an Insecure Deserialization vulnerability in Oracle WebLogic Server.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able exploit this to execute arbitrary code within the context of the application via crafted requests.
Oracle WebLogic Server 220.127.116.11 and prior
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the most recent upgrade or patch from the vendor.