NTLM Coercion Attacks: Technical Analysis and Mitigation Strategies

Introduction: The Silent Threat in Active Directory Environments

In enterprise Active Directory infrastructures, the NTLM (NT LAN Manager) authentication protocol, which has been in use for over 20 years, has become one of the most exploited vectors by cyber attackers today. NTLM Coercion attacks, especially with the discovery of techniques like PetitPotam, have emerged as a critical security vulnerability leading to domain takeover in corporate networks.

In this article, we will examine NTLM Coercion techniques in depth, explain various attack vectors, and discuss in detail the most important protection method: strategies for disabling NTLM authentication.

Fundamentals of NTLM Relay Attacks

Before understanding NTLM Coercion techniques, it's important to grasp the basics of NTLM Relay attacks. NTLM Relay is a man-in-the-middle (MITM) attack type that exploits structural weaknesses in the 20-year-old NTLMv1/2 challenge-response authentication protocol.

How NTLM Relay Works

In an NTLM Relay attack, the attacker:

1. Intercepts: Captures authentication requests from a client
2. Relays: Forwards this authentication material to a target service
3. Impersonates: The target service authenticates the attacker as the original client

Traditionally, passive protocol poisoning techniques (LLMNR, NBT-NS, mDNS) were used to initiate these attacks. However, NTLM Coercion techniques allow attackers to actively force target systems to authenticate, significantly expanding the attack surface.

Key Mitigation Strategies

The most effective protection against NTLM Coercion attacks is to completely disable NTLM authentication in your environment. This eliminates both NTLM Coercion and NTLM Relay attacks at their root.

Steps to Disable NTLM:

1. Audit current NTLM usage using Event ID 8004
2. Identify systems and applications dependent on NTLM
3. Transition to Kerberos authentication
4. Gradually disable NTLM through Group Policy

Additional Protection Measures

• Patch Management: Apply all security updates, especially for PetitPotam CVEs (CVE-2021-36942, CVE-2022-26925)
• Disable Print Spooler: Stop the service on systems where it's not needed, especially Domain Controllers
• Secure ADCS: Enable Extended Protection for Authentication (EPA) on ADCS HTTP endpoints
• SMB and LDAP Signing: Enforce signing on all systems
• Network Segmentation: Implement Microsoft's Privileged Access Workstation (PAW) model

Detection and Monitoring

Monitor for signs of NTLM Coercion attacks:

• Event ID 5145: Unexpected RPC connections
• Event ID 4776: NTLM authentication attempts
• Unusual outbound connections from Domain Controllers
• Abnormal certificate requests in ADCS logs

Conclusion

NTLM Coercion attacks pose a serious threat to modern enterprise networks. The most effective protection strategy is to completely disable NTLM authentication and transition to Kerberos. While this transition requires careful planning and gradual implementation, it fundamentally solves both NTLM Coercion and NTLM Relay attacks.

Want to test your corporate infrastructure's resilience against NTLM Coercion and other Active Directory attacks? Contact our expert team at Netlore Security for comprehensive Active Directory security assessments and penetration testing services.