This indicates an attack attempt to exploit an Insecure Deserialization Vulnerability in Rockwell Automation FactoryTalk Diagnostics.
This vulnerability is due to insufficient validation of serialized data sent to RNADiagnosticsSrv endpoint. A remote unauthenticated attacker could exploit this vulnerability by sending a crafted serialized object to the target server. Successful exploitation can result in result in arbitrary code execution under the security context of the SYSTEM.
Rockwell Automation FactoryTalk Diagnostics .
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.