Tag Archives: Exchange 2016

Exchange security updates November 2021

I have been away for a couple of days, but you already might have seen that Microsoft released a number of Security Updates for Exchange 2019, Exchange 2016 and Exchange 2013, but only for the last two Cumulative Updates (as always).

Security Updates are available for the following products:

Exchange versionDownloadKnowledge Base
Exchange 2019 CU11https://www.microsoft.com/en-us/download/details.aspx?id=103643KB5007409
Exchange 2019 CU10https://www.microsoft.com/en-us/download/details.aspx?id=103642KB5007409
Exchange 2016 CU22https://www.microsoft.com/en-us/download/details.aspx?id=103644KB5007409
Exchange 2016 CU21https://www.microsoft.com/en-us/download/details.aspx?id=103645KB5007409
Exchange 2013 CU23https://www.microsoft.com/en-us/download/details.aspx?id=103646KB5007409

The following vulnerabilities are addressed in these updates:

Security Updates are CU specific and can only be applied to the specific Cumulative Update. When trying to install a Security Update for another CU, an error message will be returned.

Security Updates are also cumulative, so this Security Update contains all previous security updates for this specific CU. There’s no need to install previous Security Updates before this Security Update.

As always, after downloading a Security Update, start the Security Update from a command prompt with elevated privileges (‘Run as Administrator’) to prevent an erratic installation. This does not apply when installing a Security Update via Windows Update or WSUS.

Exchange Quarterly Updates: Exchange 2019 CU11 and Exchange 2016 CU22

On September 28, 2021 Microsoft released their quarterly updates for Exchange server, Exchange 2019 CU11 and Exchange 2016 CU22. Despite earlier communications a new CU for Exchange 2016 is released as well.

Besides normal fixes, a new feature is introduced in these CUs as well, the Exchange Emergency Mitigation Server or EEMS. EEMS is a new service that can mitigate new security breaches when they arise. EEMS connects to a Microsoft endpoint (https://officeclient.microsoft.com/getexchangemitigations) and when needed, downloads and installs available mitigations. It performs a check once an hour. If you don’t feel comfortable with this, it is possible to disable this on an organization level 😉

Also new in Exchange 2019 CU11 and Exchange 2016 CU22 is telemetry regarding the mitigation service. When configured, it will automatically upload mitigation related service to Microsoft. Again, this can be disabled as well using the license agreement (enabled by default).

When installing this update you will see change in the License Agreement:

The default is I accept the license agreement and will share diagnostics data with Microsoft (recommended), but you can select other as well of course.

When using the unattended install, a new switch is used for accepting the License Agreement.

  • /IAcceptExchangeServerLicenseTerms_DiagnosticDataON – when you allow to upload diagnostics data to Microsoft
  • /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF – when you do not allow to update diagnostics data to Microsoft.

There are also two new prerequisites when installing Exchange 2019 CU11 or Exchange 2016 CU22. Prerequisite software contains now the ‘IIS URL Rewrite Module’ which needs to be installed. The second one is connectivity to the internet for accessing the mitigation service endpoint.

The setup application will check for these prerequisites and will generate an error when they are not met:

Note. The internet connectivity is not shown in this screenshot.

The ‘IIS URL Rewrite Module’ can be downloaded from https://download.microsoft.com/download/1/2/8/128E2E22-C1B9-44A4-BE2A-5859ED1D4592/rewrite_amd64_en-US.msi

Using PowerShell you can download the module, store it in the C:\Install directory and install it unattended using the following commands:

Start-BitsTransfer -Source "https://download.microsoft.com/download/1/2/8/128E2E22-C1B9-44A4-BE2A-5859ED1D4592/rewrite_amd64_en-US.msi" -Destination C:\Install
Start-Process -FilePath "C:\Install\ rewrite_amd64_en-US.msi " -ArgumentList "/q" -Wait

Updating the Exchange server to this latest CU is not different compared to earlier versions (except for the license agreement switch):

Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms_DiagnosticDataON
Setup.exe /PrepareAD /IAcceptExchangeServerLicenseTerms_DiagnosticDataON
Setup.exe /PrepareDomain /IAcceptExchangeServerLicenseTerms_DiagnosticDataON

Setup.EXE /Mode:Upgrade /IAcceptExchangeServerLicenseTerms_DiagnosticDataON

Note. There are no schema changes when upgrading from Exchange 2019 CU10 or Exchange 2016 CU21, but there are changes when upgrading from previous releases.

After installing the updates, you will see the new services when opening the services MMC snap-in:

Or when using the Get-Service MSExchange* PowerShell command:

To check the status in the Exchange organization, you can use the Get-OrganizationConfig | Select mitigations command:

To disable the mitigation service, execute the following command:

Set-OrganizationConfig -MitigationsEnabled:$False

By default, only one mitigation is installed, this is the EEMS heartbeat probe. You can check the installed mitigations by navigating to the Exchange scripts directory and execute the Get-Mitigations.ps1 script:

As with any Cumulative Update, please test this CU in your lab to see if all works well for your environment. Also have a look at the telemetry configuration (is that allowed in your organization?) and at the automatic configuration changes made by the EEMS (I can hear CISO starting to complain).

More information and downloads regarding the Cumulative Updates can be found here:

Microsoft Teams and Exchange 2016 connectivity

More than a year ago I wrote a blogpost regarding Teams calendaring and Exchange 2016 integration: https://jaapwesselius.com/2020/04/07/microsoft-teams-and-exchange-2016/.

Currently I am working with a customer on this specific scenario, and to my surprise I ran into this Teams/Exchange connectivity test on the Microsoft Remote Connectivity Analyzer (https://aka.ms/exRCA). Open the Remote Connectivity Analyzer, select Microsoft Teams and click the Teams Calendar Tab button. Login with the account you want to test (in this example I have an on-premises mailbox on Exchange 2019, but works for Exchange 2016 as well) and click Perform Test.

Within seconds you will see if connectivity from Microsoft Teams to your Exchange server is working properly. Very nice!

Security Updates Exchange Server December 2020

On December 8, 2020 Microsoft released a number of security updates for Exchange server. Despite the fact that Exchange 2010 is out of support at all, an important security update for Exchange 2010 was released as well.

Exchange versionKB ArticleDownload
Exchange 2010 SP3 RU31KB4593467Download
Exchange 2013 CU23KB4593466Download
Exchange 2016 CU17KB4593465Download
Exchange 2016 CU18KB4593465Download
Exchange 2019 CU6KB4593465Download
Exchange 2019 CU7KB4593465Download


  • The security updates are specific for each Cumulative Updates.
  • The upcoming CU’s for Exchange 2016 and Exchange 2019 will contain this security fix.
  • Install the security updates from an elevated command prompt.

Open attachment in Shared Mailbox using OWA

Last September Microsoft released their quarterly Cumulative Updates for Exchange, Exchange 2016 CU18 and Exchange 2019 CU7. This was quickly followed by a security update, KB4581424 that addresses the CVE-2020-16969 Microsoft Exchange Information Disclosure vulnerability.

Unfortunately, the Exchange 2016 CU18 and Exchange 2019 CU7 contain a nasty bug. If you use OWA, open a shared mailbox and try to access an attachment, OWA redirects to Office 365 instead of the on-premises Exchange 2016/2019 server to download it. This happens in an hybrid environment, but also in a pure on-premises Exchange deployment without any Office 365 connection.

The error message reads:

Hmmm… can’t reach this page
It looks like the webpage at

Microsoft is aware of this issue and it will be fixed in the next Cumulative Updates for Exchange 2016 and Exchange 2019. Looking at the quarterly cadence this should be by the end of this year.

If you have a Microsoft Premier support contract and this is an issue that impacts your business you can open a support ticket and request a fix for this. This service is available for Premier support customers only.

This fix is a replacement for the KB4581424 security update, as such it contains all the fixes in KB4581424, plus the OWA Attachment hotfix. If you are a Premier support customer and do have this fix available, make sure that you uninstall the KB4581424 first before installing this update.
One workaround that I’ve seen in a newsgroup is not to open the Shared Mailbox as “Open another mailbox” but as “Add shared folder”. This should work also, but I have not tested it. I do have a customer with a Premier support contract, I can confirm the problem is fixed in the interim update.