Windows Update KB5124012 Breaks Claude Cowork Sandbox While Logging Success
tedwuted-oss · ghdev · 2026-09-09
A developer reports that on Windows 11 ARM64, cumulative update KB5124012 (build 28000.2804 → 28000.2954) breaks Claude Cowork's sandbox VM: addplan9shares logs 'completed' but attaches no Plan9 share, so devicebash never starts. With the Claude Desktop version held constant, A/B testing showed 15/15 failures with the patch and immediate recovery after uninstalling it; the VM bundle hash was unchanged, ruling out the guest image. The author also flags a design flaw: reporting success on zero shares turns host-side failures silent.
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