Common ports, such as TCP port 80 (HTTP), may be locked down — but other ports may get overlooked and be vulnerable to hackers. In your security tests, be sure to check these commonly hacked TCP and UDP ports:

  • TCP port 21 — FTP (File Transfer Protocol)

  • TCP port 22 — SSH (Secure Shell)

  • TCP port 23 — Telnet

  • TCP port 25 — SMTP (Simple Mail Transfer Protocol)

  • TCP and UDP port 53 — DNS (Domain Name System)

  • TCP port 443 — HTTP (Hypertext Transport Protocol) and HTTPS (HTTP over SSL)

  • TCP port 110 — POP3 (Post Office Protocol version 3)

  • TCP and UDP port 135 — Windows RPC

  • TCP and UDP ports 137–139 — Windows NetBIOS over TCP/IP

  • TCP port 1433 and UDP port 1434 — Microsoft SQL Server