Port 139: NetBIOS-SSN
Port 139 is the NetBIOS Session Service, used by older Windows file sharing. Modern SMB uses port 445 directly, and port 139 is often disabled.
TCPWindowsUnencrypted by defaultIANA assigned
| Port number | 139 |
|---|---|
| Service | NetBIOS Session Service |
| Protocol | TCP |
| Category | Windows |
| Default encryption | No |
Security note. Port 139 is not encrypted by default. Restrict it to trusted networks, or use an encrypted alternative where one exists, to avoid exposing credentials and data in transit.
Frequently asked questions
What is port 139 used for?
Port 139 is the NetBIOS Session Service, used by older Windows file sharing. Modern SMB uses port 445 directly, and port 139 is often disabled.
Is port 139 TCP or UDP?
Port 139 (NetBIOS-SSN) uses TCP.
Is port 139 secure?
Port 139 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 139 on my firewall?
Only if you specifically need NetBIOS-SSN. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.