Microsoft to Deprecate NT LAN Manager in Windows 11

Microsoft has announced its plans to phase out the NT LAN Manager (NTLM) authentication protocol in Windows 11, marking a significant shift towards enhanced security. The company aims to replace NTLM with the more secure Kerberos authentication protocol, citing vulnerabilities and the need for a modernized security approach.

Understanding NTLM and Kerberos

NTLM, or New Technology LAN Manager, is a challenge-response authentication protocol that has been part of the Windows operating system since the early days. Despite its long history, NTLM is considered outdated and vulnerable to various attacks, such as pass-the-hash and relay attacks, which can compromise user credentials and system security​.

Kerberos, on the other hand, is a robust and secure authentication protocol that uses a ticketing system to authenticate users to network resources. It supports advanced encryption standards, providing better security and performance compared to NTLM. Kerberos has been the default authentication protocol for domain-connected devices on Windows versions since Windows 2000​.

Reasons for Deprecating NTLM

Microsoft’s decision to deprecate NTLM stems from its inherent security weaknesses. NTLM does not support modern encryption algorithms like AES or SHA-256, making it susceptible to sophisticated attacks. Additionally, NTLM’s reliance on a three-way handshake for authentication is less secure compared to Kerberos’ ticket-based system​​.

Despite its vulnerabilities, NTLM has persisted due to its simplicity and ease of use in certain scenarios, especially for local accounts and environments without a direct connection to a Domain Controller (DC). However, the need to transition to a more secure authentication method has become paramount as cyber threats evolve​​.

Transition to Kerberos

To facilitate the transition from NTLM to Kerberos, Microsoft is introducing two new features in Windows 11:

1. Initial and Pass Through Authentication Using Kerberos (IAKerb): This extension allows clients to authenticate with a DC through a server that has line-of-sight access, even if the client itself does not. This feature ensures secure authentication across segmented networks and remote access scenarios, protecting against replay and relay attacks.
2. Local Key Distribution Center (KDC): This feature extends Kerberos support to local accounts by using the Security Account Manager (SAM) to pass messages between remote local machines. The local KDC leverages IAKerb for secure authentication without requiring additional enterprise services​​.

Implications for Organizations

The deprecation of NTLM means organizations will need to audit their applications and services to identify where NTLM is still in use and transition to Kerberos. Microsoft recommends using existing policies and logs to track NTLM usage and implement controls to disable it where possible. Enhanced NTLM management controls will aid in this transition, allowing administrators to monitor and restrict NTLM usage within their environments​.

While NTLM will continue to be available as a fallback mechanism to ensure compatibility with legacy systems, the goal is to eventually disable it by default. Organizations are encouraged to start migrating to Kerberos to benefit from its superior security and performance​​.

Microsoft’s move to deprecate NTLM in favor of Kerberos is a significant step towards bolstering Windows 11’s security. By introducing new features to enhance Kerberos and phasing out NTLM, Microsoft aims to protect users from advanced cyber threats and provide a more secure authentication environment.