This indicates an attack attempt to exploit an Insecure Deserialization Vulnerability in Zoho ManageEngine OpManager.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request with a serialized object. A remote attacker may be able to exploit this to execute arbitrary code under the context of the root user, via a crafted request.
Zoho Corporation ManageEngine OpManager prior to 12.3 Build 123231
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: