139 NetBIOS Session / SMB over NetBIOSNetBIOS session service; legacy SMB file sharing transport.
Older SMB. Modern SMB uses 445. Block both at the perimeter.
| Transport | Status | Meaning |
|---|---|---|
| TCP | Yes | Assigned by IANA and standardized, specified, or widely used on this port. |
| UDP | Assigned | Assigned by IANA, but not standardized, specified, or widely used on this port. |
| SCTP | — | Not applicable for this transport. |
| DCCP | — | Not applicable for this transport. |
Well-known (0–1023). System port for a core service. On Unix-like systems, binding it requires superuser privileges.
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