netbios-enumeration

name

netbios-enumeration

description

Enumerate NetBIOS services (ports 137, 138, 139) to discover server names, workgroups, and MAC addresses during network pentesting. Use this skill whenever you need to enumerate NetBIOS services, discover Windows/Samba shares, investigate network name resolution, or assess NetBIOS security. Trigger this skill for any task involving NetBIOS ports, Windows network enumeration, or SMB-related reconnaissance.

NetBIOS Enumeration

Overview

NetBIOS provides three core services for network communication:

Service	Port	Protocol	Purpose
Name Service	137	UDP/TCP	Name registration and resolution
Datagram Distribution	138	UDP	Connectionless communication
Session Service	139	TCP	Connection-oriented communication

Quick Start

# Enumerate NetBIOS names and MAC addresses
nmblookup -A <IP>

# Scan a subnet for NetBIOS hosts
nbtscan <IP>/30

# Nmap enumeration with nbstat script
nmap -sU -sV -T4 --script nbstat.nse -p137 -Pn -n <IP>

Detailed Enumeration

Name Service (Port 137)

The Name Service handles name registration and resolution. Devices participate in a NetBIOS network through a broadcast process where "Name Query" packets are sent. If no objections are received, the name is considered available.

Commands:

# Query a specific host for NetBIOS names
nmblookup -A <IP>

# Scan a subnet range
nbtscan <IP>/30

# Nmap with nbstat.nse script (most comprehensive)
nmap -sU -sV -T4 --script nbstat.nse -p137 -Pn -n <IP>

What you'll discover:

• Computer/Server names
• Workgroup or domain membership
• MAC address of the network interface
• User names (sometimes visible)
• NetBIOS service types

Datagram Distribution Service (Port 138)

NetBIOS datagrams allow for connectionless communication via UDP, supporting direct messaging or broadcasting to all network names.

Check if open:

nmap -sU -p138 <IP>

Session Service (Port 139)

The Session Service facilitates connection-oriented interactions between two devices using TCP. A session begins with a "Session Request" packet and supports larger messages, error detection, and recovery.

Check if open:

nmap -sT -p139 <IP>

What to Look For

When enumerating NetBIOS, pay attention to:

1. Computer names - The NetBIOS name of the target system
2. Workgroup/Domain - Network membership information
3. MAC address - Physical network interface identifier
4. Service types - What NetBIOS services are running
5. User accounts - Sometimes visible in enumeration output

Common Nmap Findings

PORT    STATE SERVICE    VERSION
137/udp open  netbios-ns Samba nmbd netbios-ns (workgroup: WORKGROUP)
138/udp open|filtered netbios-dgm
139/tcp open  netbios-ssn  Microsoft Windows netbios-ssn

Next Steps After Enumeration

Once you've enumerated NetBIOS services, consider:

1. Check SMB vulnerabilities - Port 445 often accompanies NetBIOS
2. Attempt null sessions - Anonymous SMB connections
3. Look for password hashes - LanMan/NTLM hashes may be accessible
4. Investigate share access - Enumerate and access network shares
5. Check for misconfigurations - Anonymous access, weak permissions

Automation Script

For repeated enumeration tasks, use the bundled script:

./scripts/netbios-enumerate.sh <IP>

This runs all three enumeration methods and saves results to a file.

References

• HackTricks NetBIOS Pentesting
• NetBIOS over TCP/IP - Wikipedia