Windows update KB5124008 breaks Anthropic Cowork's sandbox shell; uninstall is the only fix
standard_deviant_Q · reddit · 2026-09-10
- Windows cumulative security update KB5124008 (build 26200.9445, installed Sep 9) breaks Cowork's sandbox on Windows: every shell command fails with sandbox-helper: no Plan9 drive shares mounted under /mnt/.virtiofs-root/shared
- File read/write via the connected folder still works; only the folder-sharing step into the Linux VM breaks. A 6am scheduled task fails the same way.
- Restart, re-adding the folder, wsl --update / wsl --shutdown did NOT help (WSL2 was healthy — Cowork's share mechanism isn't drvfs)
- Fix: wusa /uninstall /kb:5124008 in admin PowerShell, then reboot — shell came back immediately. Author paused Windows Update and set a daily check.
- Caveat: it's a security cumulative, so the workaround means staying unpatched until Anthropic ships a fix. Author asks if anyone found a way to keep the KB and still get the mount working.
More from coding & agent
- His agent kill switch ran for months before he found it was wired to nothing — AnvilandCode · 2026-09-11
- Kernel's Browser Agents Can Now Pay Online Using Aliases, Never Touching Card Data — jeff_weinstein · 2026-09-11
- OpenAI opens up agent sandboxes: BYO or pick from Cloudflare, E2B, Modal, Vercel and more — threepointone · 2026-09-11
- SocialCrawl MCP lets agents search Reddit, YouTube, TikTok, X with one API key — dooddyman · 2026-09-11
- Astra builds a surprisingly polished Catan game in three.js, reusing past UI and 3D assets — FinanceYF5 · 2026-09-11
- Open-Source Tool Highlights the Exact PDF Paragraphs Behind AI Answers — Flat-Phone-1596 · 2026-09-11