Supabase leaves 16,326 databases readable by anyone

UpGuard scanned Supabase and found 16,326 projects with tables anyone can read anonymously, reported by TechCrunch on September 25. Over half of those tables held personal data: names, addresses, phone numbers, some passwords, auth tokens, and strings that look like card numbers.

The confirmed cases are specific. Private chats from an Indian adult streaming site and a database belonging to an African consulate in France both turned up in the scan. Most of it traces to missing or weak Row Level Security, the policy that decides what an anonymous key can see.

Supabase's CISO Bil Harmer called projects secure by default and framed the rest as shared responsibility. That's accurate, but the anon key is still public by design, and only a policy someone writes stands between a table and the internet.

Supabase is the default backend a coding agent reaches for when scaffolding a full-stack app with auth. It creates the table without hesitation, but it doesn't reliably write a correct Row Level Security policy for it. I've watched agents write auth.uid() is not null as the policy check, which grants every logged-in user read access to every row.

A separate audit backs up why that keeps happening. Marmelab's audit of 246 open-source agent harness repos found 4.4% of the security rules written into public .claude/ directories have an executable check behind them. Sixty percent of the harnesses have no tests and no evals at all.

If an agent created a table for you, query it with only the anon key and see what comes back. Whatever rows return are what the rest of the internet sees too.