Microsoft: Out-of-band update against unintended server reboots

Microsoft released unplanned out-of-band updates for various Windows Server versions overnight on Monday. They are intended to resolve the problem of servers restarting unexpectedly after the April security updates were installed.

Microsoft announced the updates in the Message Center of the Windows Release Health Notes. As became known last Friday, Microsoft has acknowledged issues on Windows Servers with the security updates. Microsoft summarizes the issues as follows: A limited number of Windows Server 2025 devices may display errors when installing the April updates. In addition, after installation, domain controllers may restart repeatedly on some Windows Server versions.

Out-of-band updates

Microsoft has provided separate hotfix updates for each Windows Server version:

• Windows Server 2025 receives KB5091157
• Windows Server 23H2 KB5091571
• Windows Server 2022 KB5091575
• Windows Server 2019 KB5091573 and
• Windows Server 2016 KB5091572

Windows Servers with hotpatching enabled, i.e., “rebootless updates,” are also affected. Microsoft has also created separate hotpatch hotfixes for these.

• Windows Server 2025 Datacenter: Azure Edition Hotpatch KB5091470
• Windows Server 2022 Datacenter: Azure Edition Hotpatch KB5091576

The official designation for the hotpatching servers appears confusing. In the knowledge base entry, Microsoft explicitly mentions Windows Server 2025 with hotpatching, without further additions like Datacenter or Azure. As expected, it is available via Windows Update.

Unplanned updates: Install now

Those who uninstalled the security patches due to the issues or did not apply them at all should now quickly install the corrected updates. They partly close already exploited vulnerabilities in Windows, for example in the Edge browser and in SharePoint Server.

(dmk)