Microsoft has released security updates for vulnerabilities found in:
Exchange Server 2013
Exchange Server 2016
Exchange Server 2019
These updates are available for the following specific...
Updated May 04, 2021
Version 8.0
Blog Post
Nino_Bilic
Microsoft
MicrosoftNiels101 - Yes, apply to Edge servers too
SA - There is a specifici FAQ about Hybrid in the post; but if you are running hybrid, you are running Exchange on-premises. If you are on CU23 for Exchange 2013, you simply need to either install the April update from Microsoft Update or if you are downloading it, you MUST install the update from the elevated CMD prompt. The KB article tells you what to do (in known issues) and download instructions tell you also. It should be ~30 minutes.
Vinch_BE - yes, best is to reboot after done!
FreakyNL - unknown at this time; we do have a repro of this and engineering is looking into it. Sorry, no better answer right now!
mhincapie anthonytenherkel JazDotKiwi650 Googol GregS410 - at this time, I do not have an answer for you; I think based on error samples you have provided (thank you!), we have a good idea where to look; engineering has been engaged on this. 3rd party monitoring is something that we cannot test for in our test passes but still - if we have deliberately changed something here, we need to document it for sure. Consider this under investigation.