Microsoft released out-of-band fixes on April 19, 2026, for repeated restarts affecting some Windows Server domain controllers after the April 14 security update. The reported failure was limited to domain controllers in multi-domain forests using Privileged Access Management (PAM)—not Windows Server machines generally. The right update depends on the Server release.
What caused the Windows Server restart problem?
Microsoft said the issues were introduced by the April 2026 Windows security update. After installing that update and restarting, some domain controllers in multi-domain forests using PAM could experience startup problems. In some cases, the Local Security Authority Subsystem Service (LSASS) stopped responding, triggering repeated restarts and disrupting authentication and directory services. That could make a domain unavailable.
Microsoft also reported a separate issue: a limited number of Windows Server 2025 devices could fail to install the April update, with errors 0x800F0983 or 0x80073712. Microsoft’s announcement did not give a count or percentage of affected servers.
Microsoft described the restart issue as affecting some versions. The documented conditions are specific: a domain controller, a multi-domain forest, and PAM. The reports do not establish that ordinary servers or all domain controllers were affected. Microsoft Windows Release Health Message Center announced the fixes on April 19, 2026; the Windows Server 2025 KB5091157 article documents the technical symptoms.
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Which emergency update applies to your Windows Server?
Check the Windows Server release before selecting a package. Microsoft listed these standard out-of-band (OOB) cumulative updates and builds:
| Windows Server release | Standard OOB update | OS build | Scope stated by Microsoft |
|---|---|---|---|
| Windows Server 2025 | KB5091157 | 26100.32698 | Domain-controller restart issue and April security-update installation failures |
| Windows Server, version 23H2 | KB5091571 | 25398.2276 | Domain-controller restart issue |
| Windows Server 2022 | KB5091575 | 20348.5024 | Domain-controller restart issue |
| Windows Server 2019 | KB5091573 | 17763.8647 | Domain-controller restart issue |
| Windows Server 2016 | KB5091572 | 14393.9062 | Domain-controller restart issue |
Microsoft explicitly says the Server 2025 standard package addresses both the restart issue and update-installation failures; the other standard packages listed above address the restart issue. Confirm the release and package in Microsoft’s Release Health announcement and the support article for the matching KB before deployment.
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Azure Edition hotpatch packages are separate
The announcement also lists distinct hotpatch packages: KB5091470, build 26100.32704, for Windows Server 2025 Datacenter: Azure Edition; and KB5091576, build 20348.5029, for Windows Server 2022 Datacenter: Azure Edition. These are not the standard OOB packages in the table. Check the package’s release article and your deployment channel to determine which applies to your configuration.
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For KB5091157, Microsoft lists Windows Update, Windows Update for Business, Microsoft Update Catalog, and Windows Server Update Services (WSUS) as distribution options. The appropriate route depends on how your organization manages updates.
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- Identify the installed release. Verify whether the server runs Windows Server 2025, version 23H2, 2022, 2019, or 2016, and whether it is an Azure Edition hotpatch configuration.
- Choose the matching KB. Use the version-specific package in the table, rather than selecting by symptom alone. For other releases, follow the corresponding Microsoft support article linked from the Release Health announcement.
- Use your organization’s update channel. For KB5091157, Microsoft documents Windows Update, Windows Update for Business, Microsoft Update Catalog, and WSUS. If downloading from the Catalog, follow the KB’s instructions for MSU packages; files may need to be installed in a specified order.
- Verify deployment and recovery. Check your update-management system and server health after installation and restart. Microsoft’s release announcement establishes the intended fix, not whether a particular organization deployed it or every affected environment recovered without additional action.
The Server 2025 KB describes KB5091157 as a non-security cumulative update containing quality improvements from the April 14 update. It says previously installed updates are not downloaded again and only new updates in the package are applied. That servicing description is specific to KB5091157; check the matching article for other releases rather than assuming identical behavior. See Microsoft’s KB5091157 article for its distribution and installation details.
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What administrators should take away
- The reported restart loop followed the April 2026 security update and concerned a defined domain-controller/PAM configuration, not Windows Server broadly.
- Use the OOB KB for the exact Server release and deployment type; the standard package differs by version.
- KB5091157 for Server 2025 also addresses a limited update-installation problem. Microsoft describes the other standard packages listed here as restart fixes.
- Confirm deployment and recovery in your own management systems. Microsoft’s announcement does not establish current incident prevalence or installation status across organizations.
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