NETBIOS: Network Protocol Explained

NETBIOS (Network Basic Input/Output System) is a legacy network protocol that enables communication between computers and devices within a local area network (LAN). Originally developed by IBM in the early 1980s, NETBIOS was widely used in earlier versions of Microsoft Windows operating systems and networks. Its primary purpose is to provide a simple and straightforward method for sharing files, printers, and other resources within a LAN.

NETBIOS typically runs over transport protocols such as TCP/IP, using protocols like NBT (NetBIOS over TCP/IP) to transmit data packets. This combination allows NETBIOS to provide communication services while leveraging the underlying routing and addressing capabilities of TCP/IP.

However, in modern network environments, NETBIOS has been largely replaced by more advanced and secure technologies, such as DNS (Domain Name System) for name resolution and SMB (Server Message Block) for file and printer sharing. Additionally, the widespread adoption of Active Directory in Windows-based networks has diminished the need for NETBIOS. Despite its decline in use, some legacy systems and applications may still rely on NETBIOS for communication and resource sharing within LANs.

What is NETBIOS

NETBIOS is a legacy networking protocol designed to enable communication between computers and devices within a local area network (LAN). Developed by IBM in the early 1980s, NETBIOS was widely used in earlier versions of Microsoft Windows operating systems and networks for sharing files, printers, and other resources within a LAN.

NETBIOS is an application programming interface (API) that operates at the session layer (Layer 5) of the OSI (Open Systems Interconnection) model. It provides various services, such as name service, datagram service, and session service, to facilitate communication between devices on a network.

1. Name service (NetBIOS-NS): This service is responsible for registering, releasing, and resolving computer names to their IP addresses, enabling communication between devices on the network.
2. Datagram service (NetBIOS-DGM): It provides a connectionless communication method for sending messages or data packets between devices in a LAN without establishing a dedicated connection.
3. Session service (NetBIOS-SSN): This service facilitates connection-oriented communication between devices in a LAN, allowing the exchange of data through established sessions.

The Purpose of NETBIOS

The primary purpose of NETBIOS is to facilitate communication and resource sharing between computers and devices within a local area network (LAN). As a legacy networking protocol, NETBIOS was widely used in earlier versions of Microsoft Windows operating systems and networks. The main functions of NETBIOS include:

1. Name Resolution: The Name Service (NetBIOS-NS) component of NETBIOS is responsible for registering, releasing, and resolving computer names to their IP addresses. This allows devices on the network to communicate with each other using easily identifiable names rather than relying solely on IP addresses.
   Connectionless Communication: The Datagram Service (NetBIOS-DGM) provides a way for devices to send messages or data packets to each other without establishing a dedicated connection. This connectionless communication method is useful for sending small amounts of data, like status updates or notifications, to other devices on the network.
2. Connection-Oriented Communication: The Session Service (NetBIOS-SSN) facilitates connection-oriented communication between devices in a LAN. This allows devices to exchange data through established sessions, providing a reliable communication channel for transmitting larger amounts of data or for applications that require continuous communication between devices.
3. Resource Sharing: NETBIOS enables computers and devices on a network to share resources, such as files, printers, and other peripherals. This simplifies the process of accessing and managing shared resources within a LAN.

However, it’s important to note that NETBIOS is a legacy protocol, and its use has declined significantly with the development of more advanced and secure networking technologies.

Benefits Of NETBIOS

While NETBIOS is a legacy protocol and has largely been replaced by more modern technologies, it did offer certain benefits during its time. Some of the advantages of NETBIOS include:

1. Simplicity: NETBIOS is relatively simple to implement and configure, making it suitable for small networks and environments with limited resources. It does not require complex configuration or management, which made it appealing to administrators during its heyday.
2. Name Resolution: NETBIOS Name Service provided an easy way for computers and devices on a LAN to communicate using human-readable names instead of IP addresses. This made it more convenient for users to access resources on the network.
3. Compatibility: NETBIOS was widely used in earlier versions of Microsoft Windows operating systems and networks, which made it compatible with a large number of devices and applications.
4. Resource Sharing: NETBIOS facilitated resource sharing within a LAN, enabling computers and devices to share files, printers, and other peripherals. This simplified the process of managing and accessing shared resources.

However, it is important to note that the benefits of NETBIOS are largely overshadowed by its security and scalability limitations.

Limitations Of NETBIOS

NETBIOS, as a legacy networking protocol, has several limitations that have led to its decline in use in favor of more advanced and secure technologies. Some of the notable limitations of NETBIOS include:

1. Scalability: NETBIOS was designed for small local area networks (LANs) and does not scale well to larger networks. As the number of devices and resources in a network grows, NETBIOS becomes less efficient, leading to increased network traffic and slower performance.
2. Security: NETBIOS lacks built-in security features, making it vulnerable to various attacks, such as spoofing, man-in-the-middle attacks, and unauthorized access to network resources. Modern protocols like SMB and Active Directory offer improved security measures to protect data and network resources.
3. Limited Routing Capabilities: NETBIOS is not a routable protocol by itself, which means it is limited to communication within a single LAN. To work across different networks or over the internet, it requires encapsulation within a transport protocol like TCP/IP (using NBT, or NetBIOS over TCP/IP).
4. Reliance on Broadcasts: NETBIOS relies heavily on broadcast messages for functions like name resolution and communication, which can lead to increased network congestion and decreased performance, especially in larger networks.
5. Obsolescence: As more advanced technologies like DNS for name resolution and SMB for file and printer sharing have been developed and adopted, NETBIOS has become increasingly obsolete. These newer protocols offer better performance, security, and features, making them the preferred choice for modern network environments.

Due to these limitations, organizations have largely transitioned away from NETBIOS in favor of more secure and efficient networking protocols and technologies.

How Does NETBIOS Work

NETBIOS (Network Basic Input/Output System) works by providing a set of services that facilitate communication and resource sharing between computers and devices within a local area network (LAN). NETBIOS operates at the session layer (Layer 5) of the OSI (Open Systems Interconnection) model and typically runs over transport protocols like TCP/IP using NBT (NetBIOS over TCP/IP). Here’s an overview of how NETBIOS works:

1. Name Service (NetBIOS-NS): The name service is responsible for registering, releasing, and resolving computer names to their IP addresses. When a computer joins the network, it registers its unique NETBIOS name with the name service. This enables devices on the network to communicate using easily identifiable names rather than IP addresses. The name service uses broadcasts or unicast queries to resolve the names, and the target device responds with its IP address.
2. Datagram Service (NetBIOS-DGM): The datagram service provides connectionless communication between devices in a LAN. Devices can send messages or data packets to one another without establishing a dedicated connection. Datagram service uses the User Datagram Protocol (UDP) to transmit data packets over the network. It supports both unicast (one-to-one) and broadcast (one-to-many) communication, making it suitable for sending small amounts of data, like status updates or notifications, to other devices on the network.
3. Session Service (NetBIOS-SSN): The session service facilitates connection-oriented communication between devices in a LAN. When two devices need to exchange data, they establish a session using the session service. Once the session is established, the devices can send data to each other over the connection using the Transmission Control Protocol (TCP). The session service ensures reliable data transmission and maintains the connection until it is closed by one of the devices.

In summary, NETBIOS works by providing a set of services that enable communication and resource sharing within a LAN. It offers name resolution, connectionless communication via datagrams, and connection-oriented communication via sessions to facilitate the exchange of data between devices. However, it’s important to note that NETBIOS is a legacy protocol and has been largely replaced by more modern and secure technologies, such as DNS for name resolution and SMB for file and printer sharing.

Security Concerns Of NETBIOS

NETBIOS, as a legacy networking protocol, has several security concerns that make it less suitable for use in modern network environments. Some of the main security concerns associated with NETBIOS include:

1. Lack of Encryption: NETBIOS does not provide any built-in encryption for data transmitted between devices, leaving the data vulnerable to eavesdropping and interception by attackers.
2. No Authentication: NETBIOS does not have built-in authentication mechanisms, making it susceptible to unauthorized access, spoofing attacks, and man-in-the-middle attacks. An attacker could potentially gain access to network resources or impersonate a legitimate device on the network.
3. Broadcast Traffic: NETBIOS heavily relies on broadcast messages for various functions, such as name resolution and communication. Broadcast traffic can be easily monitored by attackers, potentially revealing sensitive information about network devices and their activities.
4. Vulnerability to Brute Force Attacks: Attackers can exploit the lack of authentication mechanisms in NETBIOS to launch brute force attacks, attempting to gain unauthorized access to network resources by guessing passwords or exploiting weak security configurations.
5. Information Leakage: NETBIOS name resolution can reveal information about the network devices, such as computer names, usernames, and shared resources. Attackers can use this information to map the network and identify potential targets for further attacks.
6. Denial of Service (DoS) Attacks: Attackers can exploit vulnerabilities in the NETBIOS protocol to launch DoS attacks, overwhelming the network with malicious traffic and rendering it unavailable to legitimate users.

Due to these security concerns, it is recommended to avoid using NETBIOS in modern network environments.

Attack Example using NETBIOS

While specific large-scale attacks exploiting NETBIOS may not have made recent headlines due to the obsolescence of the protocol, there have been historical cases where NETBIOS vulnerabilities and misconfigurations have been exploited. Two notable examples include:

1. Nimda Worm (2001): The Nimda worm was a widespread and fast-spreading computer worm that targeted Windows-based systems. It spread through multiple vectors, including email attachments, open network shares, and web servers. One of the ways Nimda propagated was by scanning for open NETBIOS shares on the local network and copying itself to those shares. This allowed the worm to spread rapidly within local networks, infecting vulnerable systems and causing significant disruption.
2. SMBRelay Attack: SMBRelay is an attack technique that exploits the NETBIOS protocol’s lack of authentication. In this attack, the attacker intercepts and relays NETBIOS authentication requests from one device to another, effectively impersonating the target device and gaining unauthorized access to its shared resources. While not a specific large-scale attack, SMBRelay is an example of how attackers can exploit NETBIOS vulnerabilities to compromise systems.

It is important to note that these examples date back to a time when NETBIOS was more widely used. In modern network environments, the use of NETBIOS has significantly declined, and more secure and advanced networking technologies have largely replaced it. However, these examples serve as a reminder of the potential risks associated with using legacy protocols like NETBIOS, emphasizing the importance of adopting more secure protocols and practices in contemporary networks.

WireX Systems NDR can help with NETBIOS Investigation

WireX Systems Ne2ition NDR (Network Detection and Response) can be a valuable tool for investigating attacks over NETBIOS. NDR solutions are designed to monitor and analyze network traffic, detect anomalies and threats, and provide insights into network activity. Here are some ways NDR can help with investigations of attacks over NETBIOS:

1. Identify Network Anomalies: Ne2ition NDR can monitor network traffic for anomalous behavior that may indicate a security threat. For example, NDR can detect unusual levels of NETBIOS traffic or unexpected NETBIOS activity that could be a sign of an attack.
2. Track Malicious Activity: Ne2ition NDR can track the behavior of malicious actors on the network, including their use of NETBIOS protocols. By analyzing network traffic, Ne2ition can identify suspicious NETBIOS activity, such as repeated failed login attempts or unusual requests for network resources.
3. Facilitate Incident Response: Ne2ition NDR can provide real-time alerts and notifications when suspicious activity is detected on the network. This can help security teams quickly identify and respond to NETBIOS-related security incidents, such as brute-force attacks or unauthorized access attempts.
4. Provide Contextual Insights: Ne2ition NDR can provide contextual insights into NETBIOS-related activity, such as the source and destination of network traffic, the types of NETBIOS requests being made, and the devices involved. This can help investigators understand the scope and impact of an attack and identify potential vulnerabilities in the network.
5. Support Compliance: Ne2ition NDR can also help organizations comply with regulatory requirements by monitoring and reporting on NETBIOS-related activity. By providing insights into network activity, Ne2ition can help organizations identify and address potential security risks and maintain compliance with relevant standards and regulations.

In summary, WireX Systems Ne2ition can play an important role in investigating attacks over NETBIOS by providing insights into network activity, detecting anomalies and threats, and supporting incident response and compliance efforts.

WireX Systems Ne2ition analyzes NETBIOS traffic, extracts the different attributes including the ones displayed below to provide in-depth visibility and context for detection, response, forensics and hunting scenarios over NETBIOS.

These attributes will also help WireX Systems map into the MITRE ATT&CK framework techniques and tactics.

MITRE ATT&CK and NETBIOS

Attacks over NETBIOS can map into several tactics and techniques of the MITRE ATT&CK framework. Here are some examples:

1. Reconnaissance (Tactic): Attackers can use NETBIOS to gather information about network devices, such as computer names, usernames, and shared resources, which can be used for further attacks.
2. Credential Access (Tactic): Attackers can use NETBIOS to launch brute force attacks against network devices, attempting to gain unauthorized access by guessing passwords or exploiting weak security configurations.
3. Discovery (Tactic): Attackers can use NETBIOS to discover information about network topology and device configurations, which can be used to plan further attacks.
4. Lateral Movement (Tactic): Attackers can use NETBIOS to move laterally within a network, spreading malware or gaining access to additional devices or resources.
5. Remote Services (Tactic): Attackers can use NETBIOS to exploit vulnerabilities or misconfigurations in remote services that rely on the protocol, such as file sharing or printer sharing.
6. Network Sniffing (Technique): Attackers can use NETBIOS to capture and analyze network traffic, potentially revealing sensitive information about network devices and their activities.
7. Protocol Tunneling (Technique): Attackers can use NETBIOS over TCP/IP (NBT) to tunnel other protocols, such as SMB, over the network, potentially bypassing network security controls.
8. Exploitation for Client Execution (Technique): Attackers can exploit vulnerabilities in client-side NETBIOS implementations to execute malicious code on target systems.

These are just a few examples of how attacks over NETBIOS can map into the tactics and techniques of the MITRE ATT&CK framework. By understanding these tactics and techniques, security teams can better identify and defend against NETBIOS-related attacks.

Conclusion

In conclusion, NETBIOS is a legacy networking protocol that was widely used in the past for communication and resource sharing within local area networks (LANs). It provides a set of services that enable devices to communicate and exchange data, including name resolution, connectionless communication via datagrams, and connection-oriented communication via sessions. However, NETBIOS has several limitations and security concerns that make it less suitable for use in modern network environments. These include its lack of encryption and authentication, susceptibility to brute force attacks, broadcast traffic, information leakage, and vulnerability to denial of service attacks.

While there have been historical cases of attacks exploiting NETBIOS vulnerabilities, the protocol is now largely obsolete, and more secure and advanced networking technologies have replaced it in modern networks. Nonetheless, it is essential to remain vigilant and adopt secure protocols and practices to prevent cyberattacks and protect network resources. Organizations should also consider deploying Network Detection and Response (NDR) solutions to monitor network activity and identify potential threats and vulnerabilities associated with legacy protocols like NETBIOS. Overall, by adopting modern networking technologies and implementing robust security measures, organizations can mitigate the risks associated with legacy protocols like NETBIOS and safeguard their networks against cyber threats.