A Bridge Too Far…. Exchange 2013 CU15

Update – 2/15/2018

There may be a change in the way that Microsoft will support upgrades from older CU’s to the latest CU of Exchange 2013 or 2016. If we review the Exchange Server Supportability Matrix we see that in the .NET section, there is this note:

    “When upgrading Exchange from an unsupported CU to the current CU and no intermediate CUs are available, you should upgrade to the latest version of .NET that’s supported by Exchange first and then immediately upgrade to the current CU. This method doesn’t replace the need to keep your Exchange servers up to date and on the latest, supported, CU. Microsoft makes no claim that an upgrade failure will not occur using this method, which may result in the need to contact Microsoft Support Services. “

Reading this it tells me that while an upgrade from an old, unsupported CU to a newer supporter is allowed, there is no guarantee it will work. If it fails, a call to Microsoft support is needed. This clarification seems to eliminate the need for the Bridge CU (CU15) and may allow for a direct path for an upgrade. I would take this note with a grain of salt as there is no guarantee it would work. This upgrade path is a hard one for Microsoft to predict as there are quite a few CUs for Exchange 2013 now and there are endless possibilities for this to fail when upgrading .NET and then upgrading to the latest CU. Proceed with caution.

Update – 11/15/2017

So a client of mine is upgrading Exchange 2013 from CU5 to CU18 this weekend. He asked what he could do to prep in order to reduce our upgrade time. The obvious one is to download all update beforehand and stage them on the servers to be upgraded. However, he was only able to get CU18 as CU15 is no longer available. So the bridge has washed out. If you need this update, you may be able to contact Microsoft? By YMMV on this one.
End of Update

Update – 9/29/2017

It appears that Microsoft has decided to leave the CU15 update as downloadable for now. Even though, as of this update, CU18 is out and only CU16 to CU18 should be out, CU15 is still available. CU14, however, has joined the ranks of the removed downloads…. I wonder how long this will last?

End of Update

For those of you who support Exchange 2013, you may be aware of the availability of CUs for Exchange 2013. If you are not, then simply put, when a new CU comes out, only that CU and the previous CU are available for Public download. There will be some interim time when the previous CU (CU-2) is also available, but that too shall pass. Currently Microsoft is now up to CU17 for Exchange 2013.

    CU – Cumulative Update – Microsoft’s quarterly update for Exchange server

What this means is that CU17 and CU16 will eventually be the only updates for Exchange 2013 out there. While CU15 is still available at the time of this post, that again shall disappear.

The Bridge

If you are running any version of Exchange 2013 that is CU14 or lower, this is going to cause you some headache if you need to update to the latest CU. Microsoft put in a .NET requirements that makes it impossible to go directly from CU14 and before to CU16 or CU17. These latest Cumulative Updates require .NET 4.6.2 BEFORE you can install them. However, CU14 and before only support up to .NET 4.6.1. See the Exchange 2013 Supportability Matrix for more information on what is supported.

According to Microsoft, the process for moving from an older to the latest CU would require 3 steps:

  • Install Exchange 2013 CU15
  • Upgrade .NET to 4.6.2
  • Install Exchange 2013 CU17

There is only one problem with this scenario. Unless you were fortuitous to have downloaded CU15 prior to the upgrade, the download for Exchange 2013 CU15 is not available from Microsoft.

Here are two scenarios that could potentially trigger this conundrum.

Scenario One
Consider the case where management has decided to pursue an investment in cloud services like Office 365. In their pursuit of this directive, the existing infrastructure was examined and a consultant brought in to help determine what upgrades need to be made to migrate to Office 265. When a health check of Exchange was performed, it was realized that the servers were far behind in their patch maintenance as Exchange 2013 CU9 is installed on all Exchange servers. According to the consultant (who knows Microsoft’s official statement), the Exchange Servers need to be CU16 or CU17 (CU17 is the latest CU for Exchange 2013).

Scenario Two
A new IT Director is hired due to lack of due diligence by the previous IT management. When this new Director arrives, a health check and survey of the existing services is ordered. It is found that patch management is lax. The Exchange server is running Exchange 2013 CU10 which is almost two years behind the latest release. As such a plan must be made in order to bring these servers back into support from Microsoft.

‘Too Far’

In both the above scenarios, the three-step process is needed in order to get to the desired end state. At some point in time, the availability of CU15 will be removed from the Public Download space. This means that if you are in either of those scenarios you would need to open up a support call with Microsoft in order to get your download:


The only real solution is to download the CU updates and store them either on a file server or in a cloud file storage service for later retrieval. At the very least you would need your current CU, CU15 and the latest CU. I would also recommend having versions of .NET available as well in case the support for those components change as well.

Final Thoughts

While I understand Microsoft’s thought process for requiring the latest updates and keeping current, the IT world is notorious for not always being up to date. Not being able to download older updates, I think, is a bit short-sighted when it comes to a major product like Exchange Server. While downloads for .NET that are over two years old and some updates for Exchange Server 2010 that are almost 4 years old can still be downloaded. We know that this policy isn’t likely to be changed as it has been in place for quite some time and not enough customers have complained about the availability. So in short, if you are still on Exchange 2013, make sure you have a copy of your current CU and CU15 if you are in this scenario.


25 thoughts on “A Bridge Too Far…. Exchange 2013 CU15

    • Thorwald, I know that CU15 has not disappeared yet. However, it will be removed in the near future. That is why I advise you to download it before it is gone…

  1. Does this mean I need to install all the CU’s since CU12 (my version) in order to get to CU17?. Aren’t these CU’s a “new” complete install of Exchange and therefore not needed to install all the old ones?

    • Brandy, The problem lies in the .NET version requirements of later versions. You do not need to install all of the CUs from CU13 to CU17 to get there. However, you will need CU15, the newest .NET and then you will be able to install CU17. Take a look at the Supportability Matrix for Exchange 2013 found HERE and it becomes apparent that there is a break around CU15. CU 16 does not support .NET 4.6.1, while CU15 supports .NET 4.6.1 and 4.6.2. This means that CU15 is your bridge to higher CUs. This is according to Microsoft’s own recommended upgrade path HERE. Hopefully that helps.

  2. Hi guys,

    just an update on this: we faced the same issue on a customer; support ticket opened and Microsoft confirmed that NOW CU 17 and later don’t require CU 15 to update .NET Framework. Long short story: if you are on CU 12, just install .NET 4.6.2 and then CU 17. This solution has been tested and applied succesfully. I think Microsoft will update KB soon. Cheers

  3. Hi there, does anyone have Exchange 2013 SP1 CU9 at all? Raised a ticket with Microsoft and apparently, testing the process in a lab to get from CU9 to CU18 is not an acceptable reason for them to provide me with CU9. Absolute Joke!

  4. Thank you for the CU15 download, you are a generous person.

    I am not sure if you can answer this question…. I have Exchange 2013 CU13, I need to get to CU19, the server already has .NET 4.7, release number from the registry says 461310 and version 4.7.02558……..so do I still have to go to CU15, then CU19? If so, none of these updates will roll my .NET back to a previous version will they…..?

    • Microsoft added a comment to their Support Matrix for Exchange that states:

      “When upgrading Exchange from an unsupported CU to the current CU and no intermediate CUs are available, you should upgrade to the latest version of .NET that’s supported by Exchange first and then immediately upgrade to the current CU. This method doesn’t replace the need to keep your Exchange servers up to date and on the latest, supported, CU.
      Microsoft makes no claim that an upgrade failure will not occur using this method, which may result in the need to contact Microsoft Support Services.”

      What that says to me is that, while you can upgrade .NET first to 4.7.1 and then to the latest CU and they will support you, there is not guarantee it will work. If it fails, you will need to call them for support. If it were me and I was on CU13 with .NET 4.7.1 installed, I would install CU19 right away and avoid any other issues with removing and adding .NET version back just to do CU15, .NET and CU19. That’s my opinion.

      • Thank you. That’s what I was thinking as well. I mean there are going to be issues either way, so why add more steps. Thanks for the advise, wish me luck 😉

  5. I just updated my Exchange 2013 server this past weekend from CU13 to CU19, and it went better than expected, I figured I would share what I did.

    First, my server is Windows 2012 R2, with Exchange 2013 single standalone, NON-DAG, and not that is matters but it’s a virtual server on VMware.

    My server already had .NET 4.7.1 so, after much research, I decided to bypass CU15, and go straight from CU13 to CU19. I followed the process that I found posted on this site:

    Near the bottom, a post from “Josh”:
    “February 17, 2018 at 1:06 am

    Thanks for the great article, Paul!

    I recently finished upgrading 6 Exchange servers from Exchange 2013 CU5 (Version 15.0 Build 913.22) to the latest Exchange 2013 CU19 successfully. The plan I followed is outlined below.

    1. Move databases
    2. Disable Certificate Revocation Check in IE
    3. Disable Anti-virus
    4. Disable backup services
    5. Put server in maintenance mode
    6. Restart server
    7. Install .NET framework 4.6.2
    8. Restart server
    9. Install Exchange 2013 CU19 with elevated permissions
    10. Restart server
    11. Verify server health (check services, check event logs, test Exchange server health w/ various PowerShell commands)
    12. Take server out of maintenance mode
    13. Move databases
    14. Test Outlook, OWA, ActiveSync, and send/receive capabilities

    Everything went very smooth and it took me about 90 minutes per server.

    Your mileage may vary and this outlined plan doesn’t nullify the need to keep our Exchange servers updated.”

    I did not have to do 1, 7, or 13 because my server is Non-DAG, but in addition, I did have to re-create my Discovery Mailbox, and reset my Perflib.

    I received no errors during the install, I hope this helps some of you:)

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