Microsoft has taken swift action to address a significant issue affecting Windows containers by releasing emergency updates for Windows Server. The problem specifically impacts containers operating under Hyper-V isolation mode, a feature that enables multiple containers to function concurrently on a single Windows host, each within its own virtual machine.
Details of the Update
The root of the issue lies in the 2025.04 B container images, which were released on April 8, 2025. Microsoft clarified that containers running in Hyper-V isolation mode could experience startup failures if their update levels did not align with that of the hosting utility virtual machine (UVM). This discrepancy led to compatibility challenges between system files, ultimately resulting in these startup failures.
With the newly deployed emergency updates, containers are now able to correctly access the essential system files from the Windows Server host. This enhancement significantly boosts both compatibility and reliability across various Windows versions.
Update Availability
On Wednesday, Microsoft rolled out out-of-band (OOB) updates for Windows Server 2019, Windows Server 2022, and Windows Server 2025 to remedy this situation. It is important to note that these updates will not be delivered through Windows Update and will not install automatically on affected servers. Instead, administrators will need to manually download the standalone MSU packages from the Microsoft Update Catalog to apply the updates.
For those looking to implement these updates, Microsoft has provided comprehensive guidance on utilizing the Deployment Image Servicing and Management (DISM.exe) tool to apply the updates to a running Windows PC or Windows installation media.
Recent Challenges and Fixes
This latest update follows a series of challenges faced by Microsoft earlier this month, where authentication issues were reported on Windows Server and Windows 11 24H2 systems. IT administrators were cautioned that restarts might render certain Windows Server 2025 domain controllers inaccessible.
Additionally, in October 2023, Microsoft acknowledged that security updates for Windows Server 2019 and Windows Server 2022 had inadvertently caused boot issues for virtual machines on Hyper-V hosts, leading to “failed to start” errors. This pattern of challenges is not new; in January and December 2022, Microsoft also released emergency updates to resolve issues that hindered the creation and startup of new Hyper-V VMs.
