This indicates an attack attempt to exploit am Information Disclosure Vulnerability in Microsoft Sharepoint Server.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote, authenticated attacker can exploit this via a crafted request, leading to disclosure of NTLM hashes.
Microsoft SharePoint Enterprise Server 2016
Microsoft SharePoint Foundation 2010
Microsoft SharePoint Foundation 2013
Microsoft Sharepoint Server 2010
Microsoft Sharepoint Server 2013
Microsoft Sharepoint Server 2019
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.