Port 139

Q: What is port 139?

Windows file sharing over NetBIOS (legacy SMB) Port 139 carries SMB (file and printer sharing) over the NetBIOS session layer, used by older Windows systems. It has been superseded by port 445, which runs SMB directly over TCP/IP. Extremely dangerous when exposed to the internet — it was a primary propagation vector for the WannaCry ransomware outbreak. This port must always be blocked at the internet perimeter.

NetBIOS-SSN

Windows file sharing over NetBIOS (legacy SMB)

Port

139

Protocol

TCP

Service

NetBIOS-SSN

Security

Dangerous

Full name: NetBIOS Session Service / SMB over NetBIOS

What is port 139?

Port 139 carries SMB (file and printer sharing) over the NetBIOS session layer, used by older Windows systems. It has been superseded by port 445, which runs SMB directly over TCP/IP. Extremely dangerous when exposed to the internet — it was a primary propagation vector for the WannaCry ransomware outbreak. This port must always be blocked at the internet perimeter.

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