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Web Security 2026-01-22 · 5 min read

Open Ports: What They Reveal and Which Ones to Close

A port is a numbered channel a server uses for a particular service — 443 for HTTPS, 22 for SSH, 3306 for MySQL. Each port that is open and reachable from the internet is part of your attack surface.

Common ports and the risk

  • 80 / 443 — web traffic; expected to be open.
  • 22 (SSH) — administration. Restrict to known IPs or a VPN; never leave it open to the world with password auth.
  • 3306 (MySQL), 5432 (PostgreSQL), 6379 (Redis), 27017 (MongoDB) — databases should never face the public internet. Exposed databases are a frequent cause of mass data breaches.
  • 21 (FTP), 23 (Telnet) — legacy and unencrypted; replace with SFTP/SSH.

Reducing exposure

Apply the principle of least exposure: close everything that does not need to be public, bind internal services to localhost or a private network, and put a firewall in front. A port scan shows which common ports respond on your host.

Put this into practice
Run a free, private scan — no login, nothing stored.
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