SMB file and print sharing, TCP 445.
Windows file servers, Samba, and macOS file sharing serve SMB2/SMB3 directly over TCP 445 — no NetBIOS session layer, unlike the legacy 137-139 ports. It carries file shares, printer shares, and named pipes used by Windows remote administration and domain traffic. It is on nearly every Windows host and any Linux box running smbd, which is why it dominates internal scans. It is also the port behind the best-known remote worm exploits (EternalBlue, WannaCry).
Do not expose
SMB must never face the internet — it exposes credentials-bearing authentication and a long history of pre-auth remote code execution; keep it inside the LAN or behind a VPN.
$ smbclient -L //TARGET -N # or: nc -vz TARGET 445
Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.