Hyper-V problem Fixed With Emergency Update

Microsoft has published an urgent emergency update for Windows Server 2025 to fix a problem that prevents Windows containers from starting. The group had previously published emergency updates for Windows 10 and 11.

Container start problems fixed in Windows Server

The unscheduled update with the identification KB5059087 for Windows Server 2025 brings the new build 26100,3781. This update specifically addresses errors in containers that are to be carried out in hyper-V isolation mode.

Technical background

According to Microsoft Knowledge Base, the out-of-band emergency update now enables containers to be able to correctly access the necessary system files of the host system. This improves reliability and compatibility between the different Windows versions.

Error description

This update fixes a problem that was caused by the 2025.04 B-container images published on April 8, 2025, in which the start of Windows containers, which is carried out in Hyper-V isolation mode, could in some cases fail if their update level did not match that of the hosting Utility Virtual Machine (and much more). Microsoft Support to KB5059087

The update is not automatically delivered via Windows Update, but is only in the Microsoft Update catalog available. Administrators must manually download the MSU file (Windows11.0-KB5059087.MSU) and can then install them via tools such as DISM (Deployment Image Servicing and Management) or Win10ui.

Further server versions also affected

The problem is not only limited to Windows Server 2025. Microsoft also provided emergency updates for older server versions: Windows Server 2022 received the Updates KB5059092 and KB5059091, while for Windows Server 2019 corresponding patches were also published.

Increasing hyper-V problems?

This is not the first time that Microsoft has to deal with hyper-V-related problems. As early as October 2023, security updates for Windows Server 2019 and 2022 led to starting problems for virtual machines at hyper-V hosts. Similar difficulties also occurred in early 2022 when emergency updates had to be published to fix problems with the creation of new Hyper-V-VMS.