139
NetBIOS Session
High RiskTCP — File Transfer
Port Overview
Port Number
139
Service Name
NetBIOS Session
Transport Protocol
TCP
Category
File Transfer
Security Risk
High
Port Range
Well-Known (0-1023)
What is Port 139?
NetBIOS Session Service. Establishes sessions for file and printer sharing on legacy Windows networks (SMB over NetBIOS). Replaced by direct SMB on port 445.
TCP
File Transfer
Commonly Used
Security Considerations
Port 139 (NetBIOS Session) is classified as high risk. This port is a common target for automated scanning and brute-force attacks. If you must expose it, restrict access to known IP addresses.
Recommendation: Use firewall rules to whitelist trusted IPs. Enable rate limiting and intrusion detection.