Hotfix for Exchange 2016 and 2019 (Apr2024)

Posted on April 23, 2024 by Michel de Rooij

Today, Microsoft released a hotfix for Exchange Server 2016 and 2016 that will not only fix some issues but, importantly, also add a much-welcomed functionality change: Hybrid Modern Authentication support OWA and ECP. You can deploy the hotfix directly on the Cumulative Update, similar to Security Updates. There is no need to deploy the March 2024 Security Update first.

The Hotfix for each supported Exchange Server build is linked below:

Exchange	Download	Build	KB	Supersedes
Exchange 2019 CU14 HU2	Download	15.2.1258.34	KB5037224	KB5036402
Exchange 2019 CU13 HU6	Download	15.2.1544.11	KB5037224	KB5036402
Exchange 2016 CU23 HU13	Download	15.1.2507.39	KB5037224	KB5036386

HMA support for OWA/ECP

This hotfix adds support for OWA and ECP when used in Hybrid Modern Authentication (HMA). This removes the need to deploy Azure Web Application Proxy for OWA and ECP when you want to deploy HMA. If you already deployed an Azure WebApp Proxy configuration for this purpose, you can choose to remove it after deploying the hotfix and configuring HMA on OWA/ECP. More information on enabling OWA and ECP for HMA support is here.

Caution: if you do not synchronize the identities of (Exchange) administrators to Entra, they will be unable to authenticate against Entra Identity and thus unable to manage Exchange on-premises using ECP. In those cases, they have the option to use Exchange Management Shell or synchronize their identities. Since Entra will be performing the authentication, you can add additional controls, such as location conditions or MFA, for those accounts.

ECC Certificate Support

The hotfix adds support for ECC certificates to Exchange, except for scenarios where Active Directory Federation Services (AD FS) is utilized. More information here.

Fixed Issues

The hotfix addresses the following issues, some of which were introduced after deploying the March 2024 SU:

Issue	Exchange 2016	Exchange 2019
Download domains not working after installing the March 2024 SU	Yes	Yes
Search error in Outlook cached mode after installing March 2024 SU	Yes	Yes
OwaDeepTestProbe and EacBackEndLogonProbe fail after installing March 2024 SU	Yes	Yes
Edit permissions option in the ECP can’t be edited	Yes	Yes
Outlook doesn’t display unread message icon after installing Exchange Server March 2024 SU	Yes	Yes
My Templates add-in isn’t working after installing Microsoft Exchange Server March 2024 SU	Yes	Yes

Notes

The hotfix is Exchange build level specific. You cannot apply the hotfix for Exchange 2019 CU14 to Exchange 2019 CU13. When downloading, the security update will carry the same name, and I would suggest tagging the file name with the Exchange version and CU when archiving it, e.g., Exchange2019-CU13-KBXXXXXX-x64-en.msp.

On a final note, as with any patch or update, it is recommended to apply this update in a test environment first, prior to implementing it in production.

Security Updates Exchange 2016-2019 (Mar2024)

Posted on March 13, 2024 by Michel de Rooij

The Exchange product group released March 2024 updates for Exchange Server 2016 and 2019.

The vulnerabilities addressed in these Security Updates for Exchange Server are:

Vulnerability	Category	Severity	Rating
CVE-2024-26198	Remote Code Execution	Important	CVSS:3.1 8.8 / 7.7

The Security Updates for each supported Exchange Server build are linked below:

Exchange	Download	Build	KB	Supersedes
Exchange 2019 CU14	Download	15.2.1544.9	KB5036401	KB5032146
Exchange 2019 CU13	Download	15.2.1258.32	KB5036402	KB5032146
Exchange 2016 CU23	Download	15.1.2507.37	KB5036386	KB5032147

OutsideInModule

Be advised that these security updates will disable Oracle Outside In Technology (OIT). Security issues have been discovered in this embedded third-party package (ADV24199947). The consequence of disabling these is that text can no longer be extracted from JPG, TIFF, and AutoCAD files for usage in Exchange Transport Rules or Data Loss Prevention rules. More information is here.

Fixed Issues

Apart from security fixes, these Security Updates also correct the following issues:

Issue Fixed	Exchange 2016	Exchange 2019
EWS search request displays inaccurate results	Yes	Yes

Notes

Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU14 to Exchange 2019 CU13. When downloading, the security update will carry the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level when archiving it, e.g., Exchange2019-CU13-KBXXXXXX-x64-en.msp.
Similar to Cumulative Updates, Security Updates are cumulative, and you only need to install the latest SU for your CU.
If you have deployed Exchange Management Tools to manage your on-premises Exchange Servers or installed the tools after removal of the Last Exchange Server for recipient management, it is recommended to apply the Security Update. Be aware of few cmdlet piping issues mentioned here.

On a final note, as with any patch or update, it is recommended to apply this in a test environment first prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates and follow a more agile approach; the ratings are an indication of the urgency.

Exchange 2019 CU14 (2024 H1)

Posted on February 13, 2024 by Michel de Rooij

The Exchange Team released Exchange Server 2019 Cumulative Update H1 2024, or CU14. Apart from the fixes, this Cumulative Update for Exchange 2019 contains the following changes:

.NET Framework 4.8.1 support on Windows Server 2022
Extended Protection will be enabled by default on the server where you installed CU14 (and later). You can override this behavior during setup or by specifying the DoNotEnableEP or DoNotEnableEPFEEWS when running setup unattended. More info on these switches, as well as the Extended Protection requirements and how to configure it, can be found here.

Unfortunately, TLS 1.3 support has been moved to CU15.

CVE-2024-21410
Enabling Extended Protection also addresses the just released CVE-2024-21410. This also applies to Exchange 2016 and even Exchange 2013 when you deployed the August 2022 Security Update on those servers and enabled Extended Protection on them.

Vulnerability	Category	Severity	Rating
CVE-2024-21410	Elevation of Privilege	Critical	CVSS:3.1 9.8 / 9.1

Download
Link to the update as well as a description of changes and fixes are below. The columns Schema and AD indicate if the CU contains Schema (/PrepareSchema) and Active Directory (PrepareAD) changes compared to the previous CU. Refer to the Exchange Schema page for schema and related versioning information. Also, to be able to manage Modern Authentication, administrators need to explicitly run /PrepareAD.

Version	Build	KB	Download	UMLP	Schema	AD
Exchange 2019 CU14	15.2.1544.4	KB5035606	Download		N	Y

Exchange 2019 CU14 fixes:

5035442 Exchange Mitigation Service does not log incremental updates
5035443 Read receipts are returned if ActiveSyncSuppressReadReceipt is “True” in Exchange Server 2019
5035444 System.argumentnullexception when you try to run an eDiscovery search
5035446 OAB shadow distribution fails if legacy authorization is blocked
5035448 MCDB fails and leads to lagged copy activation
5035450 Exchange 2019 setup installs an outdated JQuery library
5035452 Usernames are not displayed in Event ID 23 and 258
5035453 Issues in Exchange or Teams when you try to delegate information
5035455 MSExchangeIS stops responding and returns “System.NullReferenceExceptions” multiple times per day
5035456 “Deserialization blocked at location HaRpcError” error and Exchange replication stops responding
5035493 FIP-FS Proxy Customizations are disabled after a CU or an SU update
5035494 Modern attachment doesn’t work when web proxy is used in Exchange Server 2019
5035495 OWA displays junk operations even if junk mail reporting is disabled
5035497 Edit permissions option in the ECP can’t be edited
5035542 Remote equipment and room mailboxes can now be managed through EAC
5035616 Logon events failure after updating Windows Server
5035617 Transport rules aren’t applied to multipart or alternative messages
5035689 “High %Time in GC” and EWS doesn’t respond

Notes

If Cumulative Updates contain schema changes compared to the Cumulative Update you currently have deployed, you need to run Setup with /PrepareSchema. If they contain Active Directory changes, you need to run /PrepareAD. Alternatively, permissions permitting, you can let Setup perform this step. Consult the Exchange schema versions page for schema and related versioning information.
When upgrading from an n-2 or earlier version of Exchange, or an early version of the .NET Framework, consult Upgrade Paths for CU’s & .NET.
Don’t forget to put the Exchange server in maintenance mode prior to updating. Regardless, setup will put the server in server-wide offline mode post-analysis, before making actual changes.
When using Exchange hybrid deployments or Exchange Online Archiving (EOA), support requires you to trail at most one version (n-1).
Ensure the Windows PowerShell Script Execution Policy is set to Unrestricted during deployment. This to prevent installation failures due to the inability to validate script signatures.
If you want to speed up the update process for systems without internet access, you can follow the procedure described here to disable the publisher’s certificate revocation checking.
Cumulative Updates can be installed directly; no need to install RTM prior to installing Cumulative Updates.
Once upgraded, you can’t uninstall a Cumulative Update or any of the installed Exchange server roles.
The recommended upgrade order is internet-facing, non-internet-facing servers first, followed by Edge Transports.

Caution
As for any updates, I recommend thoroughly testing updates in a test environment before implementing them in production. When you lack such facilities, hold out a few days and monitor the comments on the original publication or forums for any issues.

Security Updates Exchange 2016-2019 (Nov2023)

Posted on November 14, 2023 by Michel de Rooij

The Exchange product group released November updates for Exchange Server 2016 and 2019.

The vulnerabilities addressed in these Security Updates for Exchange Server are:

Vulnerability	Category	Severity	Rating
CVE-2023-36439	Remote Code Execution	Important	CVSS:3.1 8.0 / 7.0
CVE-2023-36050	Spoofing	Important	CVSS:3.1 8.0 / 7.0
CVE-2023-36039	Spoofing	Important	CVSS:3.1 8.0 / 7.0
CVE-2023-36035	Spoofing	Important	CVSS:3.1 8.0 / 7.0

The Security Updates for each supported Exchange Server build are linked below:

Exchange	Download	Build	KB	Supersedes
Exchange 2019 CU13	Download	15.2.1258.28	KB 5032146	KB5030877
Exchange 2019 CU12	Download	15.2.1118.40	KB 5032146	KB5030877
Exchange 2016 CU23	Download	15.1.2507.35	KB5032147	KB5030877

Payload Serialization Signing

Be advised that these updates will enable payload signing by default. Payload serialization signing signs PowerShell payloads to identify possible tampering. Support for certificate-based signing of PowerShell serialization payloads got added with January security updates and is a per-server configuration. In other words, make sure you have deployed the January security updates before implementing these security updates, so your Exchange servers support payload signing before you can enable it one server at a time.

More info on the topic here. The process is explained at https://aka.ms/HC-SerializedDataSigning. To verify or configure signing, use the script published here or follow the manual steps. Signing leverages the organization-wide available Exchange Auth Certificate, which needs to be present and valid; the MonitorExchangeAuthCertificate.ps1 script can help you verify this.

Fixed Issues

Apart from security fixes, these Security Updates also correct the following issues:

Issue Fixed	Exchange 2016	Exchange 2019
Signing of the serialisation payload fails to run the few cmdlets	Yes	Yes
Unable to migrate mailbox as communication error parameter exception occurs	Yes	Yes
InvalidResponseException when you try to run Export-UMPrompt	Yes

Notes

Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU13 to Exchange 2019 CU12. When downloading, the security update will carry the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level when archiving it, e.g., Exchange2019-CU13-KBXXXXXX-x64-en.msp.
Similar to Cumulative Updates, Security Updates are cumulative, and you only need to install the latest SU for your CU.
If you have deployed Exchange Management Tools to manage your on-premises Exchange Servers or installed the tools after removal of the Last Exchange Server for recipient management, it is recommended to apply the Security Update. Be aware of few cmdlet piping issues mentioned here.

Security Updates Exchange 2016-2019 (Oct2023)

Posted on October 10, 2023 by Michel de Rooij

The Exchange product group released October updates for Exchange Server 2016 and 2019.

The vulnerabilities addressed in these Security Updates for Exchange Server are:

Vulnerability	Category	Severity	Rating
CVE-2023-36726	Elevation of Privilege	Important	CVSS:3.1 7.8 / 6.8
CVE-2023-36780	Remote Code Execution	Important	CVSS:3.1 7.2 / 6.3
CVE-2023-36778	Remote Code Execution	Important	CVSS:3.1 8.0 / 7.0

The Security Updates for each supported Exchange Server build are linked below:

Exchange	Download	Build	KB	Supersedes
Exchange 2019 CU13	Download	15.2.1258.27	KB5030877	KB5030524
Exchange 2019 CU12	Download	15.2.1118.39	KB5030877	KB5030524
Exchange 2016 CU23	Download	15.1.2507.34	KB5030877	KB5030524

TokenCacheModule

The recommendation for the August updates was to disable the TokenCacheModule in IIS to mitigate an Elevation of Privilege issue in IIS. That issue is fixed with a Windows update for CVE-2023-36434. Thus, after installing this update for IIS, it is no longer recommended to disable TokenCacheModule. When you have disabled it after installing the August 2023 updates, you can enable it again using New-WebGlobalModule -Name "TokenCacheModule" -Image "%windir%\System32\inetsrv\cachtokn.dll", or use the CVE-2023-21709.ps1 script specifying the -Rollback switch to (re-)enable it on all of your Exchange servers.

Fixed Issues

Apart from security fixes, these Security Updates also correct the following issues:

Issue Fixed	Exchange 2016	Exchange 2019
Users in account forest can’t change expired password in OWA in multi-forest Exchange deployments after installing August 2023 SU	Yes	Yes
Details Templates Editor fails and returns BlockedDeserializeTypeException	Yes	Yes
Extended Protection causes Outlook for Mac to fail to download the OAB (use updated Extended Protection script)	Yes	Yes

Notes

Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU13 to Exchange 2019 CU12. When downloading, the security update will carry the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level when archiving it, e.g., Exchange2019-CU13-KBXXXXXX-x64-en.msp.
Similar to Cumulative Updates, Security Updates are cumulative, and you only need to install the latest SU for your CU.
If you have installed the Exchange Management Tools separately for managing your on-premises Exchange Servers or installed it after removal of the Last Exchange Server for recipient management, it is recommended to apply the Security Update.