Looks like the Ubuntu VM sandbox locks down access to an allow-list of domains by default - it can pip install packages but it couldn't access a URL on my blog.
That's a good starting point for lethal trifecta protection but it's pretty hard to have an allowlist that doesn't have any surprise exfiltration vectors - I learned today that an unauthenticated GET to docs.google.com can leak data to a Google Form! https://simonwillison.net/2026/Jan/12/superhuman-ai-exfiltra...
But they're clearly thinking hard about this, which is great.
Update: I added more details by prompting Cowork to:
> Write a detailed report about the Linux container environment you are running in
https://gist.github.com/simonw/35732f187edbe4fbd0bf976d013f2...