Yes has been down for about a week now (since Oct 23). Maybe the server (http://www-cs-faculty.stanford.edu/) was taken down because of the PHP vulnerability? Let's hope it comes back up soon. If there's a specific file or page you were looking for let me know; maybe I have a saved copy :)

It's actually still accessible from computers on the local Stanford network, so someone could probably forward you a copy of whatever you're looking for. CS department affiliates recently got an email about other sites on the cs.stanford.edu subdomain not being accessible from off-campus. That email included a note "Our team is aware of the issue and is actively working toward a solution to restore access for off-campus". Unsure if it's related to recent vulnerabilities, but it wouldn't surprise me.

Separately, I know Knuth has recently mentioned drowning under a sea of (presumably LLM-found) bugs in TAOCP, so I suspect it might lead to a slight (if accidental) reprieve :)