NBT-NS (NetBIOS)

Pentesting NBT-NS - TCP/UDP Ports 137,138,139

Theory

Just like DNS, the NTB-NS (NetBIOS name service) protocol is used to translate names to IP addresses. By default, it's used as a fallback in AD-DS.

NBT-NS protocol operate on different ports depending on the type of communication:

• Port 137 (TCP/UDP): This port is used for NETBIOS Name Service

• Port 138 (TCP/UDP): This port is used for NETBIOS Datagram Service

• Port 139 (TCP): This port is used for NETBIOS Session Service. It allow SMB over NetBIOS

Practice

The tools nbtscan and nmblookup can be used for reverse lookup (IP addresses to NetBIOS names)

# Name lookup on a range
## -r: use local port 137 for scans
nbtscan -r $SUBNET/$MASK

# Find names and workgroup from an IP address
nmblookup -A $IPAdress

Some NBT-NS recon can be carried out with the enum4linux tool (see this page).

Resources

NBNS