Microsoft fixes the Windows update that broke Claude Cowork's sandbox

Your move: Install KB5129195 to restore Cowork's local sandbox on Windows

Microsoft released KB5129195, an out-of-band Windows 11 update, on September 14, 2026. It fixes the folder-sharing bug that a September 8 security update introduced for apps that manage virtual machines the way Claude Cowork does, which is what broke Cowork's local sandbox on Windows earlier this month. Microsoft names Claude Cowork among the affected apps. Installing this update restores the sandbox without needing to uninstall the earlier patch.

Why it matters

If you held off on the September 8 Windows update or worked around the broken sandbox, install KB5129195 now to get Cowork's local sandbox working again on Windows.

Source: Microsoft Support ↗

Published by Agent Log. The summary reports the linked source; “Why it matters” and the verdict are Agent Log's interpretation.

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