How to Defend Against NTLM Relay Attacks

As threats in cybersecurity change dynamically to cross the same security fences, attackers continuously look out for weaknesses in authentication systems. One of the most critical flaws is the previously mentioned NTLM relay attack, which affects the NTLM authentication protocol, which can be found on almost every Windows Environment.

This type of attack captures the authentication requests and forwards them, resulting in unauthorized access and possible data leaks. Any organization that has not put the appropriate protections in place to mitigate NTLM relay or NTLM relay attack vectors is potentially susceptible to data loss and availability loss. 

Using security measures to prevent these attacks will protect the network infrastructure and ensure the integrity of the data.

NTLM Relay Attacks Explained: Risk Mitigation

The NTLM relay is an attack type based on the NTLM authentication process. When a user attempts to authenticate, the user's credentials are sent across the network. The attackers steal these credentials and send them to another system, acting as the legitimate user. This enables them to take advantage of network resources, elevate privileges, and potentially “shift” right-to-left in the organization’s infrastructure.

NTLM relay attacks can be exploited in a number of scenarios due to misconfiguration of authentication preferences, lack of network isolation, disallowed security configuration, and legacy security settings. Such attacks lead to data breaches, system compromises, and enormous financial losses for companies.

NTLM Relay Attacks: Strengthening Network Security

It is up to organizations to mitigate such NTLM relay attacks by making sure that their authentication processes are secure and that no unauthorized credentials are used. Implementing the following security measures can help minimize the risk of exploitation.

Requiring SMB and LDAP Signing

One of the best methods to improve the defense against NTLM relay attacks is to enforce signing for SMB and LDAP. We added SMB signing, which authenticates the messages during authentication and provides protection against credential relay attacks.

We introduced LDAP signing to provide signing so that the communications can be verified before authentication. This mitigates unauthorized authentication attempts against those services and drops the analytics of NTLM relay attacks.

NTLM Blocking and Restriction Policies

Once NTLM Relay is a highly effective prey for attackers, the fundamental solution is based on a mode of mitigation, such as reconfiguring a system or server, as mentioned above, or restricting or Disabling NTLM Authentication. Administrators can create policies for Windows environments that restrict NTLM authentication use. 

The best and easiest prevention is to stop using NTLM completely and start using Kerberos authentication, which limits a significant attack vector for credential relaying attacks. Organizations need to evaluate authentication policies to improve security and ideally block NTLM.

Deploying Extended Protection for Authentication

Extended Protection for Authentication (EPA) strengthens NTLM relay attack defense by ensuring authentication requests are tied to specific sessions. This prevents attackers from relaying credentials to unauthorized systems. Enabling EPA in Windows environments enhances security by requiring authentication requests to be validated against the original requestor, preventing credential misuse.

Improving network segmentation and access controls

One of the fundamentals of NTLM relay attack mitigation is good network segmentation. It prevents attackers from easily wandering laterally across the network. The CIA triad is also often implemented in access controls, so strict access controls, such as enforcing least privilege and monitoring authentication requests, prevent unauthorized access.

Implementing Robust Monitoring and Logging Systems

Ongoing monitoring is crucial to the detection and prevention of NTLM relay attacks. Security teams can implement intrusion detection systems (IDS) and security information and event management (SIEM) solutions to monitor authentication activity. Proper logs for failed login attempts, unusual authentication behavior, and requesting access without authorization serve as early signs of an attack. Monitor actively to improve NTLM relay attack defense and react swiftly to possible threats.

NTLM Relay Attack Defense with Modern Authentication

Given this, the best method of deploying the same security against NTLM relay attacks is by implementing modern authentication protocols. Types of Challenges NTLM is being discontinued, so alternatives are better security protocols such as Kerberos authentication, certificate-based authentication, and multi-factor authentication (MFA). 

These authentication mechanisms mitigated credential relay and almost eliminated the exploitability of this attack. NTLM relay attack is another reason for organizations to upgrade their authentication systems and adopt secure authentication frameworks.

Defending Your Network

NTLM relay attacks still pose a significant security threat, enabling attackers to leverage authentication weaknesses and gain unauthorized access. Organizations lacking solid defenses against NTLM relay attacks face credential theft, network compromise, and business process interruption. 

Enforcing SMB and LDAP signing, disabling NTLM where not needed, leveraging extended protection, and tightening network segmentation are important measures to mitigate these attacks. Long-term protection against NTLM relay attacks is continuously monitored and metamorphosed to modern authentication protocols. To defend against such threats, organizations must secure their authentication processes by deploying strong security mechanisms to protect their networks.