Port
Port 139 — NetBIOS session
Port 139 (TCP) is used by NetBIOS session. NetBIOS Session Service — legacy Windows file sharing.
Port 139 at a glance
| Property | Value |
|---|---|
| Port number | 139 |
| Transport | TCP |
| Service | NetBIOS session |
| Category | Well-known port |
What it is used for
NetBIOS Session Service — legacy Windows file sharing.
Security considerations
Block externally; superseded by SMB over 445.
See our full TCP/UDP port reference and learn how firewalls filter ports in the CyberOps course.
Frequently asked questions
What is port 139 used for?
Port 139 (TCP) is used by NetBIOS session. NetBIOS Session Service — legacy Windows file sharing.
Is port 139 TCP or UDP?
Port 139 uses TCP.
Is it safe to open port 139?
Block externally; superseded by SMB over 445.
Related
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