Comprehensive Guide to Minimizing Privilege in Active Directory Security

Introduction

Active Directory (AD) is the backbone of identity and access management in most enterprise environments. However, its widespread use makes it a prime target for attackers. One of the most critical security principles in AD is minimizing privilege—ensuring users and systems have only the permissions they absolutely need.

This article explores best practices for securing AD by reducing excessive privileges, hardening configurations, and mitigating common attack vectors. We’ll cover:

Why Privileged Accounts Are a Major Target
Service Accounts: Risks and Hardening
Local Admin Rights: Balancing Usability and Security
User Rights Assignments (URAs) and Default Policies
Group Policy Delegations and Risks
Organizational Unit (OU) Permissions and Delegation
Privileged Groups: Membership and Best Practices
Kerberos Delegation: Constrained vs. Unconstrained
Exchange Permissions and Modern Alternatives
Credential Vaulting: Benefits and Limitations
User Account Control (UAC) and Split-Token Security
Monitoring and Auditing for Privileged Access

1. Why Privileged Accounts Are a Major Target

Attackers don’t always exploit vulnerabilities—they often steal credentials to move laterally. Privileged accounts (Domain Admins, Enterprise Admins, Service Accounts) are high-value targets because:

Persistence: Once compromised, attackers maintain access.
Lateral Movement: They can access multiple systems.
Data Exfiltration: They often have access to sensitive data.
Domain Compromise: Attackers can perform DCSync to extract all password hashes.

Defensive Strategy

Reduce the number of privileged accounts.
Implement Tiered Administration (Tier 0, Tier 1, Tier 2).
Use Privileged Access Workstations (PAWs) for admin tasks.
Enforce Multi-Factor Authentication (MFA).

2. Service Accounts: Risks and Hardening

Service accounts often have excessive privileges due to legacy configurations or vendor requirements.

Common Issues

Membership in Domain Admins (should never happen).
Kerberoasting Vulnerabilities (if SPNs are present).
Weak or Non-Expiring Passwords.

Best Practices

✅ Use Group Managed Service Accounts (gMSAs) where possible.
✅ Remove unnecessary SPNs to prevent Kerberoasting.
✅ Enable AES encryption for Kerberos authentication.
✅ Audit service accounts with tools like BloodHound or AD ACL Scanner.

3. Local Admin Rights: Balancing Usability and Security

Many organizations grant local admin rights for convenience, but this introduces risks:

Malware Installation: Users can accidentally install malicious software.
Credential Theft: Attackers can dump LSASS memory for hashes.

Mitigation Strategies

✔ Implement Least Privilege: Use standard user accounts for daily tasks.
✔ Use LAPS (Local Administrator Password Solution): Randomizes local admin passwords.
✔ Restrict Debug Privileges: Prevent LSASS memory dumping.

Exceptions (Developers, Help Desk)

Just-In-Time (JIT) Access: Temporary elevation via PAM solutions.
Separate Admin Accounts: No shared credentials.

4. User Rights Assignments (URAs) and Default Policies

The default Domain Controllers Policy often contains unnecessary delegations.

Critical URAs to Review

Debug Programs (should be restricted).
Backup Files and Directories (use dedicated accounts).
Allow Logon Locally (limit to admins only).

Tools for Auditing

Microsoft Security Compliance Toolkit (compare against baselines).
Policy Analyzer (identify deviations).

5. Group Policy Delegations and Risks

Attackers manipulate GPOs for persistence and privilege escalation.

Common Attack Vectors

Modifying GPOs to deploy malicious scripts.
Exploiting Group Policy Creator Owners membership.

Best Practices

🔹 Centralize GPO Management (avoid decentralized delegation).
🔹 Remove Group Policy Creator Owners (use RBAC instead).
🔹 Monitor GPO Changes with SIEM or AD auditing.

6. Organizational Unit (OU) Permissions and Delegation

OU delegations often accumulate over time, leading to excessive rights.

High-Risk Permissions

Reset Passwords (can lead to privilege escalation).
Replicate Directory Changes (DCSync).
Create/Modify User/Computer Accounts.

Remediation Steps

Use AD ACL Scanner to audit permissions.
Remove unnecessary delegations.
Implement Role-Based Access Control (RBAC).

7. Privileged Groups: Membership and Best Practices

Group	Recommendation
Domain Admins	Only for DC administration.
Enterprise Admins	Keep empty; use only when necessary.
Schema Admins	Empty unless modifying schema.
Backup Operators	Replace with dedicated service accounts.
Print Operators	No members (DCs shouldn’t host print queues).

Key Rule

No user should be a direct member of multiple privileged groups.

8. Kerberos Delegation: Constrained vs. Unconstrained

Unconstrained delegation allows a service to impersonate users across the network.

Best Practices

✔ Replace Unconstrained with Constrained Delegation.
✔ Use Resource-Based Constrained Delegation (RBCD).
✔ Mark privileged accounts as "Sensitive and Cannot Be Delegated."

PowerShell Commands to Find Risky Delegation

Get-ADComputer -Filter {TrustedForDelegation -eq $true}

Get-ADUser -Filter {TrustedForDelegation -eq $true}

9. Exchange Permissions and Modern Alternatives

Legacy Exchange permissions grant excessive AD access.

Modern Approaches

Use Split Permissions Model (separate AD and Exchange admins).
Migrate to Exchange Online (eliminate on-prem servers).
Run CleanupActiveDirectoryEMT.ps1 to remove old permissions.

10. Credential Vaulting: Benefits and Limitations

Credential vaults (e.g., CyberArk, Thycotic) help manage privileged access but don’t eliminate all risks.

Key Considerations

MFA protects vault access but not credential misuse.
Tiered access is still required (Tier 0 ≠ Tier 1).
Protected Users group prevents NTLM credential caching.

11. User Account Control (UAC) and Split-Token Security

UAC ensures admin privileges are only used when necessary.

Recommended Settings

Enable Admin Approval Mode.
Require Secure Desktop for elevation prompts.
Deny elevation requests for standard users.

12. Monitoring and Auditing for Privileged Access

Critical Actions

🔸 Enable AD auditing (monitor changes to privileged groups).
🔸 Use Defender for Identity (MDI) to detect suspicious activity.
🔸 Regularly review privileged account usage.

Final Recommendations

Audit First: Use tools like BloodHound, PingCastle, or AD ACL Scanner.
Implement Least Privilege: Remove unnecessary permissions.
Monitor Changes: Detect unauthorized privilege escalations.
Educate Teams: Ensure admins understand security implications.

By following these best practices, organizations can significantly reduce AD attack surfaces and improve their overall security posture.

This article provides a deep dive into minimizing privilege in AD. Implementing these measures will help defend against credential-based attacks and lateral movement.