Microsoft Phases Out NTLMv1: A Leap in Windows Authentication Security

In a move that secures systems while turning a significant page in authentication history, Microsoft has made decisive strides in phasing out the old and increasingly vulnerable NTLM (Net-NTLM or Windows NT LAN Manager) protocol. While many users likely missed this change amidst the flood of Windows updates, it’s an essential shift. With the latest update to Windows 11 24H2 and the upcoming Windows Server 2025, NTLMv1 has officially been removed. This change carries profound implications for administrators, developers, and users alike. Let’s dive deep into exactly what’s happening and why it matters.

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Out with the Old: NTLMv1's Retirement​

NTLM has long been a staple in Windows' authentication mechanism, dating back to the early days of Windows NT (1993). Over time, the protocol evolved with the emergence of NTLMv2, attempting to address growing vulnerabilities in the original version. However, NTLM overall has increasingly become a legacy feature. Let’s break this down:

• NTLMv1 Removal: The Windows 11 update (24H2) entirely removes NTLMv1, an authentication protocol notorious for its susceptibility to various forms of attacks, particularly credential replay and cracking attacks due to its weak cryptographic methods.
• Windows Server 2025: Similarly, Microsoft confirmed that NTLMv1 is no longer supported as of Windows Server 2025. Documentation updates now instruct IT teams to replace NTLMv1-based calls with negotiations to Kerberos or NTLMv2.

In simpler terms, this wasn’t just a vulnerability patch—it was a deliberate step to retire an outdated and insecure technology.

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Replacing NTLMv1: What's Next?​

So, what’s replacing this crusty 90s relic? Microsoft recommends shifting to Negotiate Authentication, a protocol that integrates multiple methods of secure authentication, including Kerberos. Here's how it works:

• The Negotiate Mechanism: This acts as a wrapper that attempts Kerberos authentication first. Kerberos, celebrated for its robust ticket-based system using symmetric key cryptography, is more secure and capable of scaling to modern enterprise needs.
• Fallback to NTLMv2: If Kerberos isn’t feasible (for instance, due to non-domain systems), the negotiate mechanism will fallback to NTLMv2, a significantly more secure version of Microsoft's legacy protocol. However, as companies adopt modern infrastructure, reliance on NTLMv2 should ideally diminish as well.

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Addressing the NTLM Relay Attacks: What's Changing?​

Security buffs will know that one of NTLM's glaring weaknesses lies in its vulnerability to relay attacks. In such attacks, intercepted credentials can be “relayed” to another service, granting attackers unauthorized access without actually cracking passwords.
Microsoft has introduced Extended Protection for Authentication (EPA) as a countermeasure:

1. Extended Protection: By tying authentication tokens to specific bindings (e.g., a Transport Layer Security (TLS) channel), relayed credentials cannot be reused or exploited maliciously.
2. LDAP Channel Binding: Similarly, LDAP (Lightweight Directory Access Protocol) with NTLM now incorporates mechanisms to restrict authentication to verified servers only. Attackers attempting to relay credentials to rogue servers are effectively blocked.

In plain English: Microsoft is closing the loophole that allowed NTLM relay attacks to thrive.

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Why Does NTLM Keep Getting Picked On?​

Let’s be honest: NTLM is the technology equivalent of duct tape holding together our digital infrastructures. It was never meant to support the demands or security threats we face today. Here’s why NTLM has fallen out of grace:

• Weak Encryption in NTLMv1: NTLMv1 used DES (Data Encryption Standard)-based hashing. Cracking such hashes is now trivial with modern computational power.
• Lacks Forward Secrecy: NTLM doesn’t implement forward secrecy, meaning if authentication data is stolen or compromised, attackers can retroactively decrypt past communications or misuse credentials.
• Replay Vulnerabilities: Since NTLM transmissions include hashed credentials that aren’t tied to time-sensitive or session-specific parameters, attackers can reuse intercepted hashes in a replay attack.

Such vulnerabilities make hanging on to NTLM akin to leaving your digital front door unlocked. It was only a matter of time before Microsoft took decisive action.

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What Should IT Admins and Users Do Next?​

The changes might sound trivial to everyday Windows enthusiasts, but for IT administrators managing enterprise systems, this update carries some homework. Here’s a checklist of immediate actions for organizations:

1. Audit Authentication Mechanisms: Identify systems still relying on NTLM (particularly v1). Use tools like Microsoft’s Message Analyzer to examine network traffic and authentication protocols in use.
2. Push for Kerberos Adoption: Organizations still using NTLMv1 need to prioritize migrating to Kerberos wherever possible. This may require revisiting Active Directory configurations.
3. Implement Negotiate for Legacy Systems: If Kerberos migration isn’t feasible, ensure applications fall back on Negotiate using NTLMv2 decisively and securely.
4. Harden LDAP Channels: Configure LDAP to require channel binding and use signing wherever applicable to prevent rogue server logins.
5. Communicate with Vendors: Older applications or third-party software may still rely on NTLM for compatibility. Work with vendors to update configurations or code if necessary.
6. Update Systems: If your infrastructure runs older Windows systems not receiving NTLMv1 removal patches, consider upgrading to fully benefit from Microsoft’s built-in protections.

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What Does This Mean for the Future of Windows Authentication?​

Clearly, Microsoft’s move to remove NTLMv1 reflects a broader trend: the slow but inevitable deprecation of NTLM altogether. Let’s peek into the crystal ball for a glimpse:

1. Kerberos Dominance: While Kerberos dominates Windows environments, its adoption across hybrid cloud or non-Windows platforms is increasing. Could Single Sign-On (SSO) solutions driven by Kerberos become the global standard?
2. Eliminating NTLMv2: The removal of NTLMv1 suggests NTLMv2's days may also be numbered. Enterprises are encouraged to future-proof themselves by phasing out NTLM dependencies entirely.
3. Passwordless Authentication?: Microsoft’s ongoing advocacy for passwordless, credential-based systems (like FIDO2 or biometric authentication) might ultimately replace both NTLM and Kerberos. Is this step paving the way for that future?

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Final Words: Great for Security, but an Admin Headache?​

The removal of NTLMv1 is undeniably a win for overall security hygiene. However, as is often the case, large enterprise systems built on patchwork legacy applications will feel the pinch. IT administrators will need to ensure graceful transitions without breaking their networks. For everyday Windows 11 users and small businesses, the real benefit lies in the enhanced protections against attacks like NTLM relay.
Time to breathe easier: Windows just got a whole lot safer. But for the IT pros behind the curtain, the work is far from done. So, what’s your take—an overdue security upgrade, or is Microsoft leaving legacy systems high and dry? Join the conversation below!

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Source: heise online NTLM phase-out model: Partially removed from Windows 11 24H2 and Server 2025