So it appears there is quite a big Zero Day exploit out there for Microsoft Exchange.
Microsoft has issued patches for multiple 0-day exploits and are recommending that these are patched immediately.
Microsoft are very confident that Hafnium are behind this and are actively targeting Exchange servers. Hafium is a cyber espionage group, that is said to be state sponsored from China.
You can read all the details from Microsoft - https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/
If you have Exchange then I would see about this exploit and closing off what you can ASAP.