Hardening Active Directory By Hiding Tier-0: A Practical Guide

You Should Know:

1. Hiding Tier-0 in Active Directory:

Tier-0 refers to the most critical assets in an Active Directory (AD) environment, such as Domain Controllers and Enterprise Admins.
By applying explicit Deny Read permissions on Tier-0 Organizational Units (OUs) and the AdminSDHolder object, you can limit visibility for standard users and tools like Bloodhound.
This slows down lateral movement and makes reconnaissance harder for attackers.

2. Commands for Implementing Deny Read Permissions:

Use the dsacls command to apply Deny Read permissions:

dsacls "OU=Tier0,DC=domain,DC=com" /D "DOMAIN\StandardUser:RP"

Verify permissions with:
```
dsacls "OU=Tier0,DC=domain,DC=com"
```

3. Bloodhound and Reconnaissance:

Bloodhound relies on accessible AD data. By hiding Tier-0, you reduce the effectiveness of Bloodhound queries.

Example Bloodhound query to detect Tier-0 visibility:

MATCH (n:Group) WHERE n.objectid ENDS WITH "-512" RETURN n

4. AdminSDHolder and Security Descriptors:

The AdminSDHolder object protects privileged accounts by resetting their permissions hourly.

Use the following PowerShell command to check AdminSDHolder permissions:

Get-ADObject -Identity "CN=AdminSDHolder,CN=System,DC=domain,DC=com" -Properties nTSecurityDescriptor

5. Yubikey for Tier-0 Authentication:

Implement certificate-based authentication for Tier-0 accounts using Yubikeys.

Example command to enforce smart card authentication:

Set-ADAccountControl -Identity "Tier0Admin" -SmartcardLogonRequired $true

6. Logging and Monitoring:

Enable detailed logging for Tier-0 access attempts:

Auditpol /set /subcategory:"Account Management" /success:enable /failure:enable

What Undercode Say:

Hiding Tier-0 in Active Directory is a powerful hardening technique that reduces the attack surface and slows down adversaries. However, it should be part of a layered security strategy, not the sole defense. Always test changes in a lab environment before deploying them to production. Use tools like Bloodhound to validate your configurations and ensure that critical assets remain protected. For further reading, refer to the SpookySec blog post on this topic.