Windows 11 KB5124008 Breaks Shared Folders in Hyper-V Linux VMs

A Windows 11 bug is preventing some Hyper-V-based Linux virtual machines from accessing folders shared from the Windows host. Microsoft has confirmed the issue, which can appear after installing KB5124008.

The problem affects applications that use HCS-managed virtual machines together with Plan9 for host-folder sharing.

Linux virtual machines still start normally, but Windows folders shared with the guest may not appear or may become inaccessible.

Claude Cowork and WSL are affected

Microsoft says Claude Cowork is among the applications affected by the shared-folder bug.

Windows Subsystem for Linux, or WSL, is also affected. Other software that relies on Plan9-mounted host folders inside HCS-managed virtual machines may experience the same behavior.

Applications that depend on these folders can display errors indicating that expected Plan9 drive shares have not mounted.

The issue does not necessarily prevent the Linux virtual machine itself from starting. Instead, it breaks access to files and folders that the VM expects to receive from the Windows host.

All supported Windows 11 versions are affected

The issue affects every currently supported Windows 11 client release, including Windows 11 23H2, Windows 11 24H2, Windows 11 25H2, and Windows 11 26H1.

The shared-folder problem adds to the list of issues reported around Microsoft’s September 2026 updates.

KB5124008 is also linked to Always On VPN connection failures involving certificate-based authentication.

Separately, administrators have reported Remote Desktop Services failures after the September Windows Server updates.

Microsoft is working on a fix

Microsoft says it is working on a resolution for the Plan9 host-folder sharing problem.

The company has not provided a confirmed release date for the fix, so affected users may continue seeing inaccessible shared folders until Microsoft ships an update addressing the issue.