Port 27017: MongoDB

What is port 27017 used for?

Database connections.

Is it safe to expose port 27017 to the internet?

Open MongoDB servers have been mass-ransomed. Require authentication and keep it private.

If port 27017 seems closed or unreachable

1. Check that the MongoDB service is running and listening on port 27017, not only on 127.0.0.1.
2. Check the firewall on the host itself (Windows Defender Firewall, iptables, nftables, ufw) for a rule that allows TCP 27017.
3. If the host is behind a router, confirm the forwarding rule points to the correct internal address and that your internet provider does not use carrier-grade NAT.
4. Test from outside your own network. A port can be open locally and blocked at the edge, or the other way round.

Using port 27017 safely

Treat port 27017 as an internal-only service. Reach it through a VPN or an SSH tunnel, restrict it by source address, and keep the software that listens on it patched.