NetBios Penetration Testing Fundamentals

NetBIOS (Network Basic Input/Output System) is a legacy protocol used for communication between computers in a local network. Penetration testing involves assessing the security of a network or system to identify vulnerabilities and potential exploits. When it comes to NetBIOS penetration testing, there are several fundamental aspects to consider.

137NetBIOS Name Service (NBNS)RFC 1001, RFC 1002
138NetBIOS Datagram Service (NB-DGRAM)RFC 1001, RFC 1002
139NetBIOS Session Service (NB-SESSION)RFC 1001, RFC 1002
445Server Message Block (SMB) over IPRFC 1001, RFC 1002, RFC 5661
593Microsoft DCOM (Distributed Component Object Model)N/A (proprietary)

Please note that while NetBIOS-related specifications are documented in RFC 1001 and RFC 1002, the specific RFC for the Microsoft DCOM implementation over NetBIOS is not publicly available.

It’s worth mentioning that in modern network environments, NetBIOS is considered a legacy protocol, and the use of more secure and efficient protocols like SMBv3 or SMB over TCP/IP (port 445) is recommended.

Name service for name registration and resolution (ports: 137/udp and 137/tcp).

Datagram distribution service for connectionless communication (port: 138/udp).

Session service for connection-oriented communication (port: 139/tcp).

Remember always test the default Windows credentials for old systems.
Administrator: <BLANK>
SID 5000 is admin account

Enumerate What?

As a penetration tester, when enumerating the NetBIOS protocol, there are several areas you should focus on to identify potential vulnerabilities and gather information. Here are some key aspects to consider during NetBIOS enumeration:

NetBIOS Names

Enumerate NetBIOS names to identify systems and services available on the network. This can be done using tools like NBTScan, enum4linux, or nmap with the “–script nbstat” option.

NetBIOS Shares

Enumerate shared resources (folders, printers, etc.) on NetBIOS-enabled systems. Tools like enum4linux, smbclient, or Metasploit’s auxiliary modules can assist in listing accessible shares and their permissions.

User Accounts

Enumerate user accounts through NetBIOS. This can include gathering NetBIOS-specific user information, such as usernames, SIDs (Security Identifiers), and related details. Tools like enum4linux or smbclient can help in this process.

Group Information

Enumerate NetBIOS groups and their memberships. Identify security groups, administrative groups, or any other relevant information that can assist in privilege escalation or lateral movement.

Null Sessions

Test for the presence of null sessions, which allow anonymous access to NetBIOS services. Tools like enum4linux or smbclient can be used to check for null session vulnerabilities.

Service Information

Identify the NetBIOS services running on target systems and gather information about their configurations. This can include obtaining version information, identifying vulnerable service implementations, or checking for misconfigurations that can lead to security weaknesses.

NetBIOS over TCP/IP (NBT) Records

Explore NetBIOS over TCP/IP (NBT) records in DNS to gather additional information about NetBIOS-enabled systems. Look for DNS entries related to NetBIOS names, IP addresses, or other relevant records.

NetBIOS Session Enumeration

Enumerate active NetBIOS sessions to identify established connections between systems. This can provide insights into the communication and potential attack vectors.

Without Authentication

nmblookup -A
nmap -sV --script nbstat.nse 
Nmap Netbios Scan

With Authentication

Linux Tools

enum4linuxA tool for enumerating NetBIOS information from Linux systems
smbclientAllows interaction with SMB/CIFS servers
nbtscanScans for open NetBIOS nameservers and enumerates services
nbtenumEnumerates NetBIOS names and services on a targetN/A
nmapA powerful network scanning tool that can include NetBIOS enumeration scripts

Microsoft Tools

enum4windowsA tool designed specifically for NetBIOS enumeration on Windows systems
NBTScanA command-line tool for scanning and enumerating NetBIOS information on Windows
NmapA powerful network scanning tool that can include NetBIOS enumeration scripts
ResponderA tool that listens for NetBIOS Name Service (NBNS) queries and responds to them, capturing credentials and other information
MetasploitA penetration testing framework that includes modules for NetBIOS enumeration and exploitation
  • Dsget
  • PsList
  • psloggedon
  • PsLogList
  • PsPasswd
  • PsShutdown
  • NetBIOS Enumerator

NetBios Penetration Testing

NetBIOS Name Service (NBNS) Spoofing

This vulnerability allows an attacker to spoof responses to NetBIOS name queries, redirecting traffic to their own malicious system. This can be used for various purposes, such as conducting man-in-the-middle attacks. Tools like Responder can automate this process.

NetBIOS Session Hijacking

NetBIOS sessions can be hijacked by exploiting weaknesses in the session establishment and management process. By capturing and analyzing NetBIOS traffic, an attacker can extract session-specific information or even take control of active sessions.

NetBIOS Password Cracking

Weak or default passwords used for NetBIOS authentication can be exploited through brute-forcing or password cracking techniques. This allows attackers to gain unauthorized access to systems with weak password configurations.

NetBIOS Null Session

NetBIOS allows for anonymous access known as a null session. Attackers can exploit misconfigured permissions on shares or RPC interfaces accessible through null sessions to gather sensitive information, such as user account details or system configurations.

NetBIOS Denial-of-Service (DoS)

Attackers can flood NetBIOS services with a high volume of requests, overwhelming the target system and causing it to become unresponsive. This can lead to a denial-of-service condition, disrupting normal operations.

NetBIOS Worms

Worms like Conficker (also known as Downadup) targeted NetBIOS vulnerabilities to spread across networks rapidly. These worms exploited weaknesses in NetBIOS implementations to infect vulnerable systems, creating botnets for malicious activities.

NetBIOS Exploits

NetBIOS Name Service Spoofer