Exchange 2013 Stuck CU Upgrade

During a routine update of an Exchange server, a client of mine had an issue with a Security Update for Exchange 2013 CU12. This patch, KB3184736, showed Status – Failed in the Windows Update History. After the install failed, Exchange Admin Console would not load, the Exchange Management Shell also could not connect to Exchange server, and then they noticed that all of the Exchange servers were not started.
In order to fix the same server, they then tried to update their server to CU16. When the CU16 installation complained about the .NET version, they upgraded .NET to 4.6.2. The CU16 upgrade was tried again and it failed.
Then I was called in to assist. We reviewed the situation and decided to move forward with the Exchange CU16 installation. According to Microsoft, the ideal upgrade plan would have been:

  • Upgrade Exchange 2013 CU12 to CU15
  • Update .NET to 4.6.1
  • Upgrade Exchange 2013 CU16

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