Microsoft has released Hotfix Updates (HUs) that enable support for new functionality and address issues in the March 2024 Security Update (SU).
The April 2024 HU is available for the following builds of Exchange Server:
- Exchange Server 2019 CU13 and CU14
- Exchange Server 2016 CU23
New Features
The April 2024 HU introduce support for elliptic curve cryptography (ECC) certificates and hybrid modern authentication for Outlook on the web and ECP.
Support for ECC certificates
Starting with April 2024 HU, Exchange Server 2016 and Exchange Server 2019 now support ECC certificates except when used in Active Directory Federation Services (AD FS) scenarios.
Hybrid Modern Authentication (HMA) for OWA/ECP
We are also announcing that starting with April 2024 HU, HMA for OWA/ECP is also supported. This feature requires Exchange 2019 CU14 + April 2024 HU (or later). Please see the feature documentation for more information.
Issues Addressed
The April 2024 HU also addressed issues that have been reported since the release of March 2024 Security Updates for Exchange Server. The following issues in the March 2024 SUs are addressed in this HU:
March 2024 SU issue that we still need to resolve:
- Calendar printing in OWA might not work unless CTRL+P keyboard shortcut is used. We will address this in a future update.
April 2024 Hotfix Update FAQ
This is the first HU released for Exchange Server, so to help you decide if you should install this update, we have prepared the following questions and answers:
We installed the March 2024 SU. Should we install the April 2024 HU?
The April 2024 HU is an optional update, but it does also introduce support for ECC certificates and HMA for OWA/ECP. If you installed the March 2024 SU but did not experience any of known issues and you don’t need the new functionality, you do not need to install the April 2024 HU and can wait until the future SU (which will include known issue fixes from April HU).
We did not yet install the March 2024 SU. Do we have to install the March SU first before installing the April 2024 HU?
The April 2024 HU includes the same security updates as the March 2024 SU, while addressing known issues with the March 2024 SU. If you did not install the March 2024 SU, you can install the April 2024 HU directly and skip the March 2024 SU.
Our Exchange servers update automatically through Windows / Microsoft Update. We installed the March 2024 SU already. Will our servers automatically install the April 2024 HU?
The April 2024 HU will appear as an optional update for your servers. The update is now also available on the Microsoft Update Catalog (search for KB5037224) and Windows Update.
Does the April 2024 HU contain any security updates not included in the March 2024 SU?
The security content of the April 2024 HU is the same as in March 2024 SU.
Will the two new features (support for ECC certificates and HMA for OWA/ECP) also be rolled into future updates, or must we install this specific HU to get them?
The April 2024 HU will be included in subsequent updates for Exchange Server. We are simply announcing that those two features are now supported starting with April 2024 HU.
Can April 2024 HU be uninstalled (if the need arises)?
Yes. HUs, like SUs, can be uninstalled.
Please see the March 2024 SU release blog post for installation tips and information related to security fixes included.
Documentation may not be fully available at the time this post is published.
Updates to this blog post:
- 5/6/2024: Added information that April 2024 HU is now also available on Microsoft Update Catalog and Windows Update.
The Exchange Server Team
