Microsoft has released emergency Windows Server updates to address a known issue preventing Windows containers from launching.

The issue affects only containers running under Hyper-V isolation mode, which allows multiple containers to run simultaneously on a single Windows host inside separate virtual machines.

“This update fixes an issue caused by 2025.04 B container images released on April 8, 2025 where Windows containers running in Hyper-V isolation mode could fail to start in some cases if their update level didn’t match that of the hosting utility virtual machine (UVM),” Microsoft explained.

“The mismatch caused compatibility problems between system files, leading to startup failures. With this update, containers now correctly access the necessary system files from the host, improving reliability and compatibility across different Windows versions.”

After deploying this week’s emergency updates, containers will now correctly access the necessary system files from the Windows Server host, improving compatibility and reliability across different Windows versions.

Microsoft released the following out-of-band (OOB) updates for Windows Server 2019, Windows Server 2022, and Windows Server 2025 on Wednesday to address this issue:

The updates are not delivered through Windows Update and will not install automatically on impacted servers. However, they can be installed manually after downloading the standalone MSU packages from the Microsoft Update Catalog.

Microsoft provides detailed guidance on how to use the Deployment Image Servicing and Management (DISM.exe) tool to apply the updates to a running Windows PC or Windows Installation media.

Earlier this month, the company fixed authentication issues affecting Windows Server and Windows 11 24H2 systems and warned IT admins that restarts may render some Windows Server 2025 domain controllers inaccessible.

Redmond also confirmed in October 2023 that Windows Server 2019 and Windows Server 2022 security updates released at the time broke VMs on Hyper-V hosts, causing boot issues and displaying “failed to start” errors.

One year earlier, in January and December 2022, it released emergency Windows Server updates to fix known issues causing problems creating new Hyper-V VMs and preventing them from starting.