Now that the September 2021 Cumulative Updates (CUs) for Exchange Server 2019 and Exchange Server 2016 have been released, customers around the world now have access to a new security feature in Exch...
Updated Oct 01, 2021
Version 1.0
Blog Post
We have been happily using the mitigation service for some time, and all of a sudden it stopped working for us with the following error:
Message=Exception encountered while fetching mitigations : This XML is not deemed safe to consume since Response xml''s signing cert is invalid or not from microsoft'
I decided to inspect the X509 certificates being sent in the request on the https://officeclient.microsoft.com/getexchangemitigations URL, and I noticed that the "Microsoft Exchange XML Signing" certificate expired on the 9th June:
So I think someone needs to update that at Microsoft! 