UDP Port 139 – NetBIOS Session Service (SMB over NetBIOS)

About UDP Port 139

The Internet Assigned Numbers Authority (IANA) registers port 139 for netbios-ssn. The IANA description reads: ‘NETBIOS Session Service’. This port appears in 1 IDS rule and does not have notable malware activity indicators in our data.

IDS Rule References

1 IDS / security rule reference UDP port 139. Treat that number as context, not a danger score. Many detection rules are written against groups of ports rather than one service, web ports especially, so common web alternate ports inherit large counts while genuinely sensitive services can show few rules or none. Presence in IDS rules does not mean traffic on this port is malicious.

Rule categories (top 1): attempted-recon (1).

Sample rule descriptions for UDP port 139:

• ET SCAN Nessus Netbios Scanning

Data Sources

This information is compiled from: IANA Service Name and Transport Protocol Port Number Registry, Emerging Threats Open Ruleset (BSD 2-Clause / GPLv2 per SID range), Snort Community Rules (GPLv2), and MITRE ATT&CK (Apache 2.0).