Active Directory Security Best Practices

Securing your Active Directory (AD) environment is paramount to protecting your organization's sensitive data and resources. This document outlines key security principles, configurations, and best practices for maintaining a robust AD security posture.

1. Principle of Least Privilege

The principle of least privilege dictates that users and applications should only have the minimum necessary permissions to perform their intended tasks. This significantly reduces the attack surface and limits the damage that can be caused by compromised accounts.

• User Accounts: Assign users to groups based on their roles and responsibilities. Avoid granting direct administrative privileges to standard user accounts.
• Service Accounts: Configure service accounts with the minimal permissions required for the service to run. Use Group Managed Service Accounts (gMSAs) where possible for enhanced security.
• Administrative Privileges: Implement Just-In-Time (JIT) and Just-Enough-Administration (JEA) models for administrative tasks to further restrict access.

2. Strong Password Policies

Enforcing strong password policies is a fundamental layer of defense against brute-force attacks and credential stuffing.

• Complexity Requirements: Mandate minimum length, use of uppercase and lowercase letters, numbers, and special characters.
• Password History: Prevent users from reusing old passwords.
• Account Lockout: Configure account lockout thresholds and durations to deter repeated failed login attempts.
• Password Expiration: Regularly enforce password changes.

3. Regular Auditing and Monitoring

Continuous auditing and monitoring of AD activity are crucial for detecting suspicious behavior and potential security breaches early.

Key Audit Events to Monitor:

• Account logons (successes and failures)
• Account management (creation, deletion, modification)
• Group membership changes
• Policy changes
• Privileged account usage
• Directory service access

Utilize tools like Windows Event Viewer, Microsoft Sentinel, or third-party SIEM solutions to centralize and analyze these logs.

4. Secure Domain Controllers

Domain controllers (DCs) are the most critical components of your AD infrastructure. Protecting them should be a top priority.

• Physical Security: Ensure DCs are located in secure, access-controlled physical environments.
• Network Segmentation: Isolate DCs on a dedicated network segment with strict firewall rules.
• Limited Software Installation: Install only essential software and services on DCs.
• Regular Patching: Keep DCs up-to-date with the latest security patches from Microsoft.
• Restrict Remote Management: Limit remote administrative access to DCs and use secure protocols like RDP with Network Level Authentication (NLA).

5. Implementing Group Policy Objects (GPOs)

GPOs are powerful tools for enforcing security settings across your AD environment.

Examples of Security-Focused GPOs:

• Enforcing password policies
• Configuring audit policies
• Restricting the execution of unauthorized software
• Managing firewall rules
• Disabling unnecessary services
• Controlling USB drive access

6. Protecting Against Malware and Ransomware

While not solely an AD security issue, AD plays a role in defending against and recovering from malware attacks.

• Antivirus/Anti-malware: Deploy and maintain up-to-date endpoint protection solutions.
• Regular Backups: Implement a robust backup strategy for your AD data and system state. Test restoration procedures regularly.
• User Education: Train users to recognize phishing attempts and avoid suspicious links or attachments.

7. Understanding and Managing Trust Relationships

If your AD environment spans multiple forests or domains, carefully manage trust relationships.

• Scope of Trusts: Only establish trusts where absolutely necessary and configure them with the appropriate direction and transitiveness.
• Auditing: Regularly audit and review existing trust relationships.

8. Secure DNS Configuration

DNS is a critical service for AD name resolution. Securing it prevents DNS spoofing and cache poisoning attacks.

• DNSSEC: Implement DNS Security Extensions where supported.
• Forwarder Security: Configure forwarders carefully and consider using trusted public DNS servers or internal DNS solutions.
• Zone Transfer Restrictions: Limit zone transfers to authorized servers.

Conclusion

Active Directory security is an ongoing process that requires vigilance, regular review, and adaptation to evolving threats. By implementing the principles and practices outlined in this document, organizations can significantly strengthen their AD security posture and protect their valuable digital assets.