• 👉 Overview
• 👀 What ?
• 🧐 Why ?
• ⛏️ How ?
• ⏳ When ?
• ⚙️ Technical Explanations
• Step 1: Initiate the Negotiation
• Step 2: The Challenge
• Step 3: The Authentication
• 🖇️ References

👉 Overview

👀 What ?

Windows Force NTLM Privileged Authentication is a security feature of Microsoft's Windows operating system that forces certain user accounts to use NTLM (NT LAN Manager) authentication. NTLM is a suite of Microsoft security protocols meant to provide authentication, integrity, and confidentiality to users.

🧐 Why ?

This feature is essential because it helps protect sensitive data and systems from unauthorized access. By forcing privileged accounts to use NTLM authentication, Windows adds an extra layer of protection. This is because NTLM is a challenge-response authentication protocol, which means it doesn't send password credentials in plaintext over the network. Instead, it uses a three-way handshake, making it harder for attackers to gain unauthorized access.

⛏️ How ?

To implement this feature, you need to navigate to the 'Local Security Policy' on your Windows system. From there, go to the 'Security Settings' -> 'Local Policies' -> 'Security Options'. Look for the policy named 'Network security: Force NTLMv2 session security if negotiated' and enable it.

⏳ When ?

The practice of forcing NTLM privileged authentication started with the introduction of the NTLMv2 protocol with Windows NT 4.0 Service Pack 4 in 1996. It has since become a standard security measure in Windows systems.

⚙️ Technical Explanations

The NTLM (NT LAN Manager) is a suite of Microsoft security protocols used to provide authentication, integrity, and confidentiality to users. The authentication process of NTLM is conducted in three distinct steps: the negotiation, the challenge, and the authentication phase.

In the negotiation phase, the client and the server establish the communication settings, setting the ground rules for how the rest of the process will proceed. This involves the client sending an initial message to the server, which will then respond with the acceptable settings.

Following this, the challenge phase begins. During this stage, the server generates and sends a challenge to the client. This challenge is essentially a nonce, or a random number that can be used just once in a communication session. The client must respond to this challenge with a proof of identity. This proof is generated by hashing the user's password with the nonce.

The final step is the authentication phase. Here, the server receives the client's response from the challenge phase. It verifies this proof by independently calculating the expected response using the stored hashed password of the client and the nonce it issued during the challenge phase. If the client’s response matches the server’s calculated value, the authentication is successful.

Windows Force NTLM Privileged Authentication is a feature that requires certain privileged accounts to use this process. By enforcing this, it adds a significant layer of security as it prevents password credentials from being transferred in plaintext over the network. However, while this feature does enhance security, it is not entirely foolproof and should be considered part of a wider suite of security measures. It is important to keep systems updated and follow best practices for password security and management.

To provide a detailed example, let's consider a scenario where an administrator account on a Windows Server 2016 wants to authenticate itself to access resources on a network.

Step 1: Initiate the Negotiation

The client initiates the process by sending a NEGOTIATE_MESSAGE to the server. This message contains information about the highest NTLM version that the client supports, and may look something like this:

NTLMSSP\\x00\\x01\\x00\\x00\\x00\\x07\\x32\\x00\\x00

The NTLMSSP is the signature of the message, \\x01 is the message type (negotiate message), and \\x07\\x32 is the flags (indicating NTLMv2).

Step 2: The Challenge

The server, upon receiving the NEGOTIATE_MESSAGE, sends a CHALLENGE_MESSAGE back to the client. The challenge message includes a server challenge (nonce). It might look something like:

NTLMSSP\\x00\\x02\\x00\\x00\\x00\\x0c\\x00\\x0c\\x00\\x38\\x00\\x00\\x00\\x01\\x82\\x00\\x00\\x01\\x23\\x45\\x67\\x89\\xab\\xcd\\xef\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00

Here, NTLMSSP is the signature, \\x02 is the message type (challenge message), and 01\\x23\\x45\\x67\\x89\\xab\\xcd\\xef is the server challenge.

Step 3: The Authentication

The client generates the NTLMv2 response using the server challenge and the user's password. The client sends this response in an AUTHENTICATE_MESSAGE. An example of the response would be:

NTLMSSP\\x00\\x03\\x00\\x00\\x00\\x18\\x00\\x18\\x00\\x6c\\x00\\x00\\x00

In this case, NTLMSSP is the signature, \\x03 is the message type (authenticate message), and the rest of the message contains the client's hashed response to the server challenge.

The server, upon receiving the AUTHENTICATE_MESSAGE, validates the client's response against its expected hashed value. If the client’s response matches the server’s calculated value, the authentication is successful.

This process, enforced by the Windows Force NTLM Privileged Authentication feature, adds an additional layer of security. However, it should be noted that this is not a substitute for other necessary security measures such as secure password practices and keeping the system updated.

🖇️ References