Active Directory secure by design: Building resilience from the ground up

Active Directory wasn’t built with today’s threat landscape in mind. When Microsoft released Active Directory with Windows 2000, the primary concerns were directory services functionality and network efficiency – not defending against sophisticated nation-state actors or ransomware groups. Yet here we are in 2025, with Active Directory serving as the backbone of enterprise identity management while simultaneously being the crown jewel that attackers relentlessly pursue.

The challenge isn’t just patching vulnerabilities or adding security controls after the fact. It’s fundamentally rethinking how we approach Active Directory security through the lens of “secure by design”: a philosophy that bakes security considerations into every architectural decision from day one.

Understanding secure by design principles

Secure by design means integrating security as a core requirement throughout the entire system lifecycle, rather than treating it as an add-on feature. This approach shifts security from reactive to proactive, from bolt-on to built-in.

Traditional security approaches often follow a pattern: deploy the system, discover vulnerabilities, apply patches, repeat. Secure by design flips this model by anticipating threats during the design phase and building controls that make successful attacks significantly harder to execute.

For complex systems like Active Directory, this means examining each component (from forest architecture to group policy design) through a security lens before implementation.

Why Active Directory needs secure by design thinking

Active Directory remains one of the most attacked resources in enterprise environments, and for good reason. A compromised domain controller doesn’t just give attackers access to user accounts – it provides the keys to your entire digital kingdom.

The fundamental challenge is that Active Directory was designed for a different era. Many of its default configurations prioritize backward compatibility and ease of administration over security hardening. Domain controllers communicate over unencrypted channels by default, legacy authentication protocols remain enabled, and administrative privileges are often distributed far too broadly.

Modern attackers exploit these design decisions systematically. They use techniques like Kerberoasting, Golden Ticket attacks, and DCSync to move laterally through networks and establish persistent access. These aren’t vulnerabilities in the traditional sense, they’re features of Active Directory that become security liabilities without proper hardening.

Secure by design for Active Directory architecture

Forest and domain design

Your Active Directory forest architecture sets the security foundation for everything that follows. A secure by design approach means treating security boundaries as hard boundaries from the start.

Consider implementing a dedicated administrative forest separated from your production environment. This “Red Forest” model ensures that even if your production domain is compromised, attackers can’t automatically pivot to your most privileged accounts.

Within domains, apply the principle of least privilege to organizational unit (OU) design. Create OUs that reflect your security requirements, not just your organizational chart. This makes it easier to apply targeted group policies and reduces the risk of privilege creep over time.

Network segmentation and domain controller placement

Domain controllers should never sit directly on your production network. Implement network micro-segmentation to isolate DCs and require explicit firewall rules for communication.

Place domain controllers in dedicated VLANs with restricted access. Only allow the specific ports and protocols required for AD functionality – typically TCP 389 for LDAP, TCP 636 for LDAPS, TCP 88 for Kerberos, and a few others. Block everything else by default.

Implementing secure by design for Active Directory authentication

Moving beyond NTLM

Legacy authentication protocols like NTLM present significant security risks. A secure by design approach implements modern authentication protocols and disables legacy options where possible.

Audit your environment to identify systems still using NTLM authentication. Develop a migration plan to move these systems to Kerberos, then systematically disable NTLM across your domain. This single change eliminates entire categories of attacks, including pass-the-hash and NTLM relay attacks.

Kerberos hardening

Even Kerberos requires hardening to meet secure by design principles. Enable AES encryption for Kerberos tickets and disable weaker encryption types like DES and RC4. Configure appropriate ticket lifetimes – shorter lifetimes reduce the window for Golden Ticket attacks but may impact user experience.

Implement Kerberos armoring (FAST) to protect authentication exchanges from offline attacks. This adds an additional layer of encryption around Kerberos messages, making them significantly harder for attackers to intercept and crack.

Administrative access controls

Tiered administration model

Maintaining a minimal number of privileged users and using groups to assign privileges forms the cornerstone of secure AD administration.

Implement a tiered administrative model that separates privileges based on risk levels:

• Tier 0: Domain controllers and enterprise-level systems
• Tier 1: Servers and server applications
• Tier 2: Workstations and user devices

Administrators should have separate accounts for each tier they manage, and these accounts should never cross tier boundaries. This prevents lateral movement if any single administrative account is compromised.

Just-in-time administration

Traditional “always-on” administrative privileges violate secure by design principles. Instead, implement just-in-time (JIT) administration using tools like Microsoft’s Privileged Access Management (PAM) or third-party solutions.

JIT ensures that administrative privileges are only active when needed and automatically expire after a defined period. This dramatically reduces the attack surface and limits the potential impact of compromised administrative credentials.

Group policy security

Security-first policy design

Group Policy Objects (GPOs) should enforce security settings by default, not as an afterthought. Create a baseline security GPO that applies strong security configurations across all systems, then use additional policies for specific requirements.

Key security settings include disabling unnecessary services, configuring Windows Firewall rules, enabling audit logging, and enforcing secure authentication protocols. Link security GPOs at the domain level to ensure they can’t be accidentally bypassed.

Regular policy auditing

Implement automated tools to regularly audit your group policy configuration for security drift. Policy settings can change over time due to administrative errors or business requirements, potentially creating security gaps.

Password security as a secure by design foundation

Weak passwords remain one of the most common attack vectors against Active Directory. A secure by design approach treats password security as a fundamental architectural requirement, not a user training problem.

The built-in Active Directory password policy provides basic protection but falls short of modern security requirements. It can’t block commonly used passwords, dictionary words, or passwords that have been exposed in data breaches.

This is where specialized tools become essential. Solutions like Specops Password Policy extend Active Directory’s native capabilities by screening passwords against databases of known compromised credentials and enforcing organization-specific password rules. By continuously scanning for over 4 billion known compromised passwords, you can prevent prevent attackers from using credential-based attacks to gain initial access to your environment.

The integration happens at the domain controller level, ensuring that every password change is evaluated against current threat intelligence before being accepted. This approach transforms password policy from a compliance checkbox into an active security control.

Monitoring and detection

Security-focused logging

Configure comprehensive audit logging across all domain controllers. Enable detailed logging for authentication events, privilege changes, group modifications, and policy changes. Store these logs in a centralized SIEM solution for analysis and alerting.

Focus on detecting attack patterns rather than individual events. For example, multiple failed Kerberos pre-authentication attempts might indicate an ASREPRoasting attack, while unusual service ticket requests could signal Kerberoasting.

Behavioral analytics

Implement behavioral analytics to detect subtle signs of compromise. Look for unusual logon patterns, unexpected privilege escalations, or administrative actions outside normal business hours.

These analytics become particularly powerful when combined with machine learning algorithms that can establish baseline behaviors and alert on deviations.

Maintenance and continuous improvement

Secure by design isn’t a one-time implementation—it’s an ongoing commitment to security excellence. Regular security assessments should evaluate your AD configuration against current best practices and emerging threats.

Conduct annual purple team exercises that specifically target Active Directory. These exercises help validate your security controls and identify areas for improvement before real attackers do.

Keep your domain controllers patched and up to date. Microsoft regularly releases security updates that address newly discovered vulnerabilities in Active Directory components.

Building a more secure future

Active Directory secure by design requires a fundamental shift in thinking. Instead of asking “How do we secure our existing AD implementation?” the question becomes “How do we build AD security that’s resilient by design?”

This approach demands more upfront planning and potentially higher initial costs, but the long-term benefits are substantial. Organizations with mature secure by design implementations experience fewer security incidents, faster incident response times, and lower overall security management costs.

The threat landscape will continue to evolve, but organizations that embrace secure by design principles for Active Directory will be better positioned to defend against both current and future attacks. Start with the fundamentals—strong authentication, proper privilege separation, and comprehensive monitoring—then build additional controls on that foundation.

Your Active Directory doesn’t have to be the weakest link in your security chain. With the right approach, it can become one of your strongest defenses.

Start your secure by design journey today

Ready to transform your Active Directory password security from a compliance requirement into an active defense mechanism? Specops Password Policy integrates directly with your existing AD infrastructure to block over 4 billion known compromised passwords and enforce custom password rules that align with your security requirements.

Unlike basic group policy settings, Specops Password Policy evaluates every password change against real-time threat intelligence, preventing credential stuffing attacks before they can gain a foothold in your environment. It’s secure by design thinking applied to one of your most critical attack vectors. Let’s discuss your specific requirements – book a live demo today.