UDP Port 137 – NetBIOS Name Service (NetBIOS-NS)

About UDP Port 137

Port 137 carries the IANA assignment for netbios-ns. The IANA description reads: ‘NETBIOS Name Service’. This port appears in 6 IDS rules and does not have notable malware activity indicators in our data.

IDS Rule References

6 IDS / security rules reference UDP port 137. 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 2): attempted-admin (5), attempted-recon (1).

Sample rule descriptions for UDP port 137:

• NETBIOS NS lookup response name overflow attempt
• NETBIOS NS lookup short response attempt
• OS-WINDOWS name query overflow attempt UDP
• 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), and Snort Community Rules (GPLv2).