This indicates an attack attempt to exploit an Insecure Deserialization Vulnerability in SolarWinds Patch Manager.
The vulnerability is due to insufficient validation of user-supplied JSON data submitted to the WSAsyncExecuteTasks.aspx endpoint. A remote, authenticated attacker can exploit this vulnerability by sending a crafted request to the target system. Successful exploitation results in remote code execution under the security context of NETWORK SERVICE.
SolarWinds Patch Manager 2020.2.5 and earlier
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.