Analysis Summary

Microsoft has released hotfix updates to address multiple known issues affecting Exchange servers after installing the March 2024 security updates. The April 2024 Hotfix Update (HU) is optional but introduces support for ECC certificates and Hybrid Modern Authentication (HMA) for Outlook on the Web (OWA) and Exchange Control Panel (ECP).

Users who have installed the March 2024 Security Update (SU) and haven't encountered any known issues or don't require the new features can wait for the next Exchange Server SU, which will include these hotfixes. The April 2024 HU includes the same security updates as the March 2024 SU and addresses known issues with it. If the March 2024 SU hasn't been installed, users can directly install the April 2024 HU.

This month's hotfixes resolve various issues caused by the March 2024 security updates. These include problems with download domains affecting Outlook, leading to issues with inline images and attachments in OWA. Additionally, errors such as "We can't open this document" in OWA and blocked Microsoft Word document previews in Outlook on the Web have been addressed. Other issues fixed include search errors in Outlook cached mode, failures of OwaDeepTestProbe and EacBackEndLogonProbe, inability to edit permissions option in the ECP, missing unread envelope icon in Outlook, malfunctioning My Templates add-in, and errors with published calendars.

The April 2024 hotfixes are compatible with Exchange Server 2019 CU13 and CU14, as well as Exchange Server 2016 CU23. Microsoft announced the end of mainstream support for Exchange Server 2019 in January but will continue releasing patches for security issues until further notice. Exchange Server 2016 is under extended support until October 2025. Migration guidance for Microsoft 365 is available on the company's documentation site to assist global admins in deciding the migration path to Exchange Online.

Overall, Microsoft's latest updates aim to address critical issues and enhance the stability and functionality of Exchange servers, offering options for users to either install the April 2024 HU or wait for future updates depending on their needs and circumstances.

Impact

• Gain Access

Remediation

• Use Microsoft Automatic Update to apply the appropriate patch for your system, or the Microsoft Security Update Guide to search for available patches.
• Install the latest updates and hotfixes from Microsoft to fix known issues and enhance security.
• See if the new features in the updates are useful for your organization and install them if needed.
• Keep an eye on your Exchange system after updates to catch any new issues early.
• If you encounter any problems listed in the update notes, follow Microsoft's instructions to solve them.
• Since support for older versions is ending, start planning to move to Microsoft 365 or Exchange Online.
• Keep up with regular maintenance and updates to keep your Exchange system running smoothly and securely.