I have a question related to the current Exchange vulnerabilities: I run an Exchange server 2016 with CU15. Since the installation of the security patch required a more recent CU, I tried to install CU19 but the system threw a "System.UnauthorizedAccessException” at step 16 of 18 which is “Mailbox role: client access front end service”. I already tried to reinstall CU19 but it does not seem to be possible. Since CU19 was not successfully installed, I still cannot install the security patch.
Since a few days, there is also a security patch for CU15 available. However, the system detects CU19 so I am also unable to install this patch.
Is there any option to repair CU19 or how would you suggest proceeding? The ultima ratio would be to fully reinstall the entire Exchange server but cannot imagine that is the most efficient way.