CU12 Exchange 2016 and .NET 4.7.2

CU Exchange Server

We are nearly done with installing CU12 Exchange 2016 on our Exchange servers. We had CU8 in place before. This CU requires the C++ redistributable 2013 package to be installed.



One of the main issues CU12 Exchange 2016 addresses:

Exchange Web Services Push Notifications can be used to gain unauthorized access

Another fix which can be very useful regarding disk space addresses this one :

Disable the irrelevant Query logs that are created in Exchange Server 2019 and 2016

A whole list of fixes can be found here.

Further CU12 acts as a bridge for us to update our .NET version from 4.7.1 to 4.7.2 which is required to upgrade to Exchange 2019 later on.

Check the supportability matrix from Microsoft below and verify your .Net version. When you have CU7 or lower and .NET 4.6.2 in place you will need an additional round to upgrade to .NET 4.7.1 with CU8 or higher.

CU12 Exchange 2016 SupportabilityMatrix

In our test environment running CU11, we installed .NET 4.7.2 first and wanted to install CU12 Exchange 2016 afterward. This broke the server! Sometimes it happened that open processes were blocking the install. Options:

  • Restart the server
  • Stop all matching monad.exe ( find with PID ) processes.
  • Stop the IMAP and POP service while in maintenance mode.

Order of install: Win Patches, CU12 Exchange 2016, .NET 4.7.2

CU12 Exchange 2016 can break additional configurations you have defined in the EWS web.config file. For example we have added the key add key=”UseDisabledAccount” value=”1″ to the OWA and to the EWS web.config.
This key helps with the correct handling of low-level calendar permissions as AvailabilityOnly and LimitedDetails on security groups when working with resource forests ( linked mailboxes ).
After CU12 has been installed this key was not present in the EWS web.config anymore. It turned out when a customer reported that users who want to access a resource calendar are not able to open it in Outlook and OWA.
Make a backup of your relevant web.config files and verify the current web.configs after the install.

You can find a description of how to install a CU here: CU Install Exchange 2016

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