What is Windows New Technology LAN Manager (NTLM)?

Windows New Technology LAN Manager (NTLM) is a suite of Microsoft security protocols that provides authentication, integrity, and confidentiality to users. NTLM is the successor of the LAN Manager (LM) authentication protocol and was initially introduced in Windows NT operating systems. It has since been an integral part of Windows environments and is sometimes referred to as NT LAN Manager.

What Is NTLM Used For?

NTLM is primarily employed as a network authentication protocol, enabling users to authenticate their identity when accessing resources within a Windows domain. It is also widely used in other applications and services, including Exchange Server, Internet Information Services (IIS), and SharePoint. NTLM authentication allows users to access resources and services securely without repeatedly entering their credentials.

How Does NTLM Authentication Work?

NTLM operates as a Challenge/Response authentication mechanism, which follows a three-step process to authenticate users:

  1. Negotiation: The client initiates the authentication process by sending a Type-1 message to the server, indicating its supported NTLM features and capabilities. The server acknowledges the message and responds with a Type-2 message, containing the server’s supported features and a challenge (nonce).
  2. Challenge: The client takes the server’s challenge and combines it with the user’s credentials, creating an encrypted NTLM hash. This hash is then sent back to the server as a Type-3 message, which contains the user’s username, domain, and encrypted response to the challenge.
  3. Authentication: Upon receiving the Type-3 message, the server validates the user’s response by comparing it with its stored hash of the user’s credentials. If the responses match, the server confirms the user’s identity and grants access to the requested resources.

The NTLM protocol leverages various hashing and encryption algorithms, such as MD4 and RC4, to ensure the confidentiality and integrity of authentication data.

What Are the Security Concerns Around NTLM?

Despite its widespread use, NTLM has several security vulnerabilities and limitations:

  • Pass-the-Hash attacks: NTLM stores user credentials in the form of hashed values, which are susceptible to Pass-the-Hash attacks. In these attacks, adversaries can capture the NTLM hash and use it to impersonate a legitimate user without needing to decrypt the actual password.
  • Brute force attacks: NTLM hashes are vulnerable to brute force attacks, in which attackers systematically attempt different password combinations to discover the correct credentials.
  • Relay attacks: NTLM is also susceptible to relay attacks, where an attacker intercepts the authentication process and forwards messages between the client and server, potentially gaining unauthorized access to resources.

The inherent security limitations of NTLM have led to the development and adoption of more secure authentication protocols, such as Kerberos.

What’s the Difference Between NTLM and Kerberos?

While both NTLM and Kerberos are authentication protocols used in Windows environments, they differ in several key aspects:

  • Authentication mechanisms: NTLM uses a Challenge/Response authentication process, while Kerberos employs a ticket-based system. In Kerberos, clients receive a ticket-granting ticket (TGT) from the Key Distribution Center (KDC) after initial authentication, which they can use to request service tickets for accessing specific resources. This process minimizes the exposure of user credentials during authentication.
  • Security features and vulnerabilities: Kerberos provides mutual authentication, reducing the risk of relay attacks, which are prevalent in NTLM. Additionally, the ticket-based approach in Kerberos mitigates the risk of Pass-the-Hash attacks, making it more secure than NTLM.
  • Performance and scalability: Kerberos offers better performance and scalability, thanks to its reliance on a centralized KDC. This centralized system simplifies authentication management in large networks, whereas NTLM may struggle in such environments due to its peer-to-peer nature.
  • Compatibility and integration: NTLM is compatible with older Windows systems, while Kerberos is primarily designed for more modern environments. However, most Windows systems support both protocols, allowing for smooth integration and migration between the two.


While NTLM has played a crucial role in Windows environments for many years, it has become outdated due to its security vulnerabilities and limitations. The introduction of Kerberos has led to a more secure and scalable authentication solution, better suited for modern network environments. As a result, Microsoft has been gradually replacing NTLM with Kerberos as the default authentication protocol for its products and services. Organizations are encouraged to migrate to Kerberos to ensure improved security and performance in their Windows networks.

Ready to go Passwordless?

Indisputable identity-proofing, advanced biometrics-powered passwordless authentication and fraud detection in a single application.