Docker Bypasses UFW — How to Fix Firewall Rules Properly
You set up UFW. You configured default deny incoming, opened only ports 22 and 443. You checked ufw status verbose — everything looks right. Then you spin up a Postgres container publishing port 5432, and suddenly port 5432 is open to the whole internet. Your UFW rules didn’t stop it. This isn’t a bug. Docker modifies iptables directly in ways that bypass user-level firewall tools like UFW. Every docker run -p creates a raw iptables DNAT rule that sits above UFW’s INPUT chain. The result: containers are exposed regardless of your UFW policy. ...