Microsoft AD Trusts from a Security Perspective

SEC-NET = Secure Network
LESS-NET = The Less Secure Network

When it comes to setting up domain trusts between networks with varying levels of security, it is crucial to be careful to maintain the security and integrity of the more secure network, in this case, SEC-NET.

In this scenario, a one-way trust would be ideal. This would be set up such that the secure network, SEC-NET, trusts the less secure network, LESS-NET. This means that the authentication requests are initiated from SEC-NET to access resources in LESS-NET, but not the other way around. LESS-NET cannot initiate authentication requests to access resources in SEC-NET.

This setup minimizes the risk of the LESS-NET being able to compromise the SEC-NET since it cannot authenticate or access resources in the more secure network. It also provides some level of integration between the two networks as users from SEC-NET can still access resources in LESS-NET when needed.

From a security perspective, there are several issues that should be taken into consideration:

  • Trust direction: It is important to establish trust in the correct direction, i.e., from SEC-NET to LESS-NET. Reversing the direction would expose the secure network to unnecessary risks.
  • Least privilege principle: Even though a trust relationship exists, it’s important to strictly manage what resources users from SEC-NET can access in LESS-NET to minimize potential exposure to security vulnerabilities.
  • Monitoring and Auditing: Regularly monitoring and auditing the authentication requests and transactions across the trust will help in identifying any suspicious activities early and take necessary action.
  • Patch Management: Ensure that both networks are regularly updated with the latest security patches to minimize vulnerabilities that could be exploited.
  • Firewall Configuration: Firewalls should be properly configured to only allow necessary traffic from SEC-NET to LESS-NET and vice versa.
  • PCI Compliance: If SEC-NET handles cardholder data and needs to be PCI compliant, remember that any system connected to it (directly or indirectly) could impact its compliance status. You may need to demonstrate that LESS-NET cannot compromise the cardholder data environment in SEC-NET, even if there’s a trust relationship.

Remember that while a one-way trust provides a higher level of security than a two-way trust, it is not foolproof. Additional security measures should always be in place to protect the integrity and confidentiality of the data in both networks.


What do I mean by no FoolProof:

When I say that a one-way trust is not foolproof, I mean that while it does provide a certain level of security, it does not completely eliminate all security risks. There are still potential vulnerabilities that could be exploited despite the presence of a one-way trust. Some of these risks include:

  • Insider Threats: A malicious insider on the SEC-NET network could potentially use their access to compromise LESS-NET. Since SEC-NET trusts LESS-NET, an insider might move laterally from SEC-NET to LESS-NET and then attempt to use that trust relationship to escalate their privileges or access.
  • Less Secure Network Vulnerabilities: Even though LESS-NET cannot initiate access to SEC-NET, if LESS-NET is compromised (due to being less secure), an attacker could potentially exploit the trust relationship to gain unauthorized access to SEC-NET resources that can be accessed from LESS-NET.
  • Misconfiguration: Incorrectly configuring the trust or any related network and security settings could inadvertently leave vulnerabilities that could be exploited.
  • Transitive Trust: If LESS-NET has trust relationships with other networks, this could expose SEC-NET to additional risks. An attacker could exploit these relationships to move laterally from network to network.
  • Unpatched Vulnerabilities: If systems within either network are not regularly updated with the latest security patches, they could have vulnerabilities that can be exploited to compromise the trust relationship.

So, while a one-way trust is a good starting point for securing the communication between two networks with different security levels, it’s crucial to also have other security measures in place. These could include regular security auditing and monitoring, robust firewall configurations, timely patch management, rigorous access controls, and a strong security policy.


Examples Less Secure Network Vulnerabilities with a couple of scenarios:

Example 1: Manipulating Trust for Lateral Movement

Let’s assume there’s a file server in LESS-NET that users from SEC-NET frequently access due to the trust relationship. An attacker who has compromised LESS-NET could place malicious scripts or software on this server. When a user or a service from SEC-NET accesses this file server, the malicious script could be executed in the context of SEC-NET, thereby providing the attacker a foothold in the secure network.

Example 2: Privilege Escalation via Service Accounts

Consider a scenario where a service account from SEC-NET is used to access a database on LESS-NET. If an attacker manages to compromise LESS-NET and capture the credentials of this service account, they could potentially use these credentials to authenticate back to SEC-NET under the context of the service account, potentially gaining more access or privileges than a regular user.

Example 3: Man-in-the-Middle Attacks

Consider that LESS-NET has been compromised and an attacker is able to monitor and manipulate the network traffic within that network. When a user from SEC-NET initiates a connection to a server on LESS-NET, the attacker could intercept and alter the traffic (man-in-the-middle attack). This could lead to a variety of issues, such as capturing sensitive data, injecting malicious code, or even establishing a connection back to SEC-NET under the guise of a legitimate user.

Example 4: Exploiting Vulnerable Software

Suppose there is a web application hosted on LESS-NET that users from SEC-NET frequently use due to the trust relationship. If this web application has known vulnerabilities (like SQL injection, Cross-Site Scripting, etc.), an attacker who has compromised LESS-NET could exploit these vulnerabilities. By doing so, they could capture the session tokens or credentials of a user from SEC-NET and then use these to access resources within SEC-NET.

Example 5: Phishing or Social Engineering Attacks

If an attacker has access to LESS-NET, they could use that access to conduct more convincing phishing or social engineering attacks on users from SEC-NET. For example, they could send a phishing email that appears to be from a legitimate user or server within LESS-NET. Because of the trust relationship, users from SEC-NET may be more likely to fall for this sort of attack.


These scenarios and examples illustrate that even with a one-way trust where LESS-NET cannot directly authenticate into SEC-NET, vulnerabilities or compromises in the less secure network can still pose significant risks to the more secure network. The exploitation of these vulnerabilities can provide an indirect attack pathway into SEC-NET. This emphasizes the critical importance of implementing robust security measures, enforcing the principle of least privilege, and consistently monitoring for suspicious activities across all networks, regardless of the trust relationships in place. Thus, securing all networks and trust relationships becomes imperative in maintaining a robust and resilient security posture.