This indicates an attack attempt to exploit an Elevation of Privilege vulnerability in Microsoft Exchange Server.
The vulnerability is due to an error when the vulnerable software handles a series of maliciously crafted HTTP requests. A remote attacker may be able to exploit this to escalate their privileges on vulnerable systems.
Microsoft Exchange Server 2019
Microsoft Exchange Server 2016
Microsoft Exchange Server 2013
Privilege Escalation: Remote attackers can leverage their privileges on vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.