After 25 years of supporting enterprise identity management, on-premises Active Directory (AD) remains central to many organizations’ security infrastructure. However, as a solution architect who’s helped numerous companies improve AD security through identity transformations, I’ve witnessed firsthand how years of incremental changes, acquisitions and evolving best practices have inadvertently created security vulnerabilities in many Active Directory environments.
But here’s the good news: A well-planned migration — whether consolidating multiple domains after acquisitions or transitioning to Microsoft Entra ID — presents an ideal opportunity to dramatically strengthen your Active Directory security posture and reduce your attack surface.
The evolving challenge of Active Directory security
Active Directory security is essential for protecting identities and safeguarding your organization’s most critical information. Yet many organizations face significant challenges in maintaining robust AD security for several reasons:
Most Active Directory deployments have been upgraded and modified as best practices evolved over the decades, but it’s rare for organizations have completely redesigned their infrastructure from the ground up. This evolutionary approach often creates security gaps as configurations accumulate over time.
Many of the IT professionals who established Active Directory environments have retired or moved on. Younger team members may have more experience with cloud solutions like Entra ID than with on-premises Active Directory. This knowledge gap about why certain configurations were implemented can put organizations at a disadvantage when securing, migrating, or modernizing their identity infrastructure.
Common Active Directory security vulnerabilities
Through numerous assessments and migration projects, I’ve consistently encountered two critical categories of AD security vulnerabilities:
Poorly configured administrative accounts: One of the most common issues involves administrative accounts that were set up with improper security practices. High-privileged accounts with full access rights connected to servers create significant risk. Attackers can compromise these servers using different accounts and extract cached credentials, potentially gaining broad access to your environment.
Complex and misconfigured Group Policy Objects (GPOs): GPOs present another major vulnerability. These policies have often been configured and modified over many years, creating complex interdependencies and security gaps. Common issues include:
- Improper certificate configurations
- GPOs configured to allow management by unauthorized users
- Excessive privileges assigned to accounts within the environment
Perhaps most concerning are scenarios where domain controller synchronization was enabled for legitimate reasons but configured in ways that expose credential information to potential attackers. This can lead to credential theft that enables brute force attacks against your environment.
Improving AD security by migrating to Entra ID
Migrating to Entra ID offers a strategic opportunity to address these accumulated vulnerabilities while modernizing your identity infrastructure. By default, nearly all modern environments (98-99%) connect both Active Directory and Entra ID, creating two potential attack vectors for adversaries. While you can implement security measures for both, the most effective approach is to reduce your attack surface by consolidating to the newer solution.
Moving identity management to Entra ID brings several security advantages:
- Modern security approaches and technologies
- Automated security updates from Microsoft
- Reduction in on-premises infrastructure requiring manual patching
- Simplified management through cloud-based tools
For organizations that have grown through acquisitions, consolidating multiple Active Directory forests eliminates the need for complex, manually-maintained directory synchronization between environments. This simplification not only improves security but also reduces operational overhead.
Addressing hybrid environment challenges
While cloud migration offers compelling security benefits, certain scenarios still require maintaining some on-premises Active Directory presence. For example, I’ve worked with customers in manufacturing environments that still require machinery operating on isolated, on-premises scenarios. In these cases, properly isolating these systems and implementing strict access controls remains essential for true AD security.
Another situation I’ve encountered over the years are legacy, hard-coded applications with outdated authentication methods. These scenarios may still require on-premises Active Directory. When full cloud migration isn’t feasible, consider:
- Implementing cloud authentication for most users while maintaining hybrid identity for specific use cases
- Applying modern security policies from the cloud to on-premises environments
- Transitioning from traditional Group Policies to modern management solutions like Microsoft Intune
Steps for mitigating risks during Active Directory migrations
Any migration involves temporary exposure, making security during the transition particularly important. Here are the essential steps to ensure your AD security remains robust throughout the process:
1. Protect privileged migration accounts
Migration processes require elevated privileges to function properly. Treat migration accounts and devices as Tier 0 assets — your digital crown jewels — and implement rigorous monitoring and protection. These accounts should adhere to the most up-to-date security models available.
2. Avoid common security pitfalls
One of the most misunderstood aspects of Active Directory migrations involves SID history. While enabling SID history can make transitions more convenient for users, it introduces significant security concerns because these legacy identifiers are rarely audited properly. Similarly, establishing trusts between environments can create hidden vulnerabilities.
For optimal Active Directory security:
- Avoid migrating passwords when possible
- Minimize use of SID history
- Limit establishment of trusts between environments
- Implement proper access controls in target environments
3. Test and plan for secure transitions
Maintaining business continuity while enhancing Active Directory security requires thorough testing and planning:
Application authentication assessment: Before migration, test all applications to determine their authentication requirements. For applications that can’t authenticate against modern identity systems, you’ll need to either:
- Replace them with modern alternatives
- Create isolated environments for legacy applications
- Implement secure hybrid authentication methods
Minimizing user disruption: For successful adoption, the migration should minimize disruption to end users’ workflows. Properly planned migrations ensure that:
- Users remain productive throughout the transition
- Familiar work environments are maintained where possible
- New security measures don’t impede legitimate business processes
This user-centric approach requires careful planning to determine how many users can be supported during each migration phase.
4. Follow security frameworks and standards
Organizations should align their Active Directory security practices with established frameworks like the NIST Cybersecurity Framework. These guidelines provide valuable best practices for reducing security risks, including recommendations for identity modernization.
While some organizations struggle to fully implement these guidelines due to legacy application constraints, migration projects offer an opportunity to move closer to compliance by transitioning to more easily updated cloud environments.
Looking forward: The future of identity security
Microsoft’s strategic direction clearly signals a cloud-first approach, with many on-premises security applications reaching end-of-life status. If your organization relies on Microsoft technologies, you should consider this trajectory when planning your identity security roadmap.
The inevitable retirement of experienced Active Directory administrators over the next 5-10 years presents another compelling reason to modernize identity infrastructure. By migrating to cloud-based solutions that younger IT professionals are more familiar with, organizations can address both security and staffing challenges.
Conclusion
Active Directory security remains fundamental to protecting your organization’s identities and critical information. While years of incremental changes have created security vulnerabilities in many environments, migrating to Entra ID creates the perfect opportunity to implement more robust security measures and reduce your attack surface.
By addressing common vulnerabilities, implementing modern security practices and aligning with established security frameworks, you can transform what might seem like a purely technical exercise into a strategic security initiative.
In an era of increasingly sophisticated threats, using migrations to enhance Active Directory security isn’t just good practice — it’s an essential strategy for modern identity protection.
