This indicates an attack attempt to exploit a Remote Code Execution Vulnerability in Microsoft SharePoint Server.
The vulnerability is due to improper validation when parsing a control markup. A remote attacker could exploit this vulnerability by creating and invoking a specially crafted Web Part. Successful exploitation results in the execution of arbitrary code in the context of service account.
Microsoft SharePoint Foundation 2013 Service Pack 1
Microsoft SharePoint Server 2019
Microsoft SharePoint Enterprise Server 2016
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.