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Introduction:
Active Directory (AD) remains the backbone of identity and access management for the vast majority of enterprises worldwide, making it the single most attractive target for ransomware gangs and nation-state actors. A compromised Domain Controller is essentially a “Game Over” for an organization’s network security. While the concepts of AD management may seem routine, the execution of proper hardening techniques is often neglected, leaving networks vulnerable to privilege escalation and lateral movement. This article transforms a standard best-practice checklist into a technical deep dive, providing the specific commands and configurations required to fortify your on-premises identity infrastructure.
Learning Objectives:
- Implement technical controls to minimize the Active Directory attack surface by auditing and removing unused objects.
- Enforce the principle of least privilege through command-line tools and Group Policy to mitigate credential theft.
- Establish monitoring and disaster recovery procedures to detect anomalies and ensure business continuity post-breach.
You Should Know:
1. Mastering Permission Inheritance and Delegation
Before blindly changing permissions, you must understand the scope of inheritance. Breaking inheritance incorrectly can orphan OUs, preventing users from logging in.
– What it does: Inheritance allows permissions set at a parent OU (e.g., “Company Users”) to flow down to child objects (e.g., “Sales Team”). Blocking inheritance creates a barrier but increases administrative overhead.
– Step-by-step guide:
1. Open Active Directory Users and Computers (ADUC) .
2. Navigate to View and ensure Advanced Features is checked.
3. Right-click an Organizational Unit (OU) > Properties > Security tab > Advanced.
4. To block inheritance, click Disable inheritance. You will be prompted to either convert inherited permissions into explicit permissions or remove them entirely.
5. Command Line Alternative: To view inheritance status on a specific OU using PowerShell:
Get-ADOrganizationalUnit -Identity "OU=Sales,DC=undercode,DC=local" -Properties | Select-Object -Property Name, DistinguishedName, @{Name="InheritanceEnabled";Expression={$_.ntSecurityDescriptor.AreAccessRulesProtected -eq $false}}
2. Hardening Default Configurations via Group Policy
Default settings in Windows Server are often configured for ease of setup, not security. Attackers routinely exploit legacy protocols like NTLMv1 or LLMNR.
– Step-by-step guide (Disabling LLMNR):
1. Open Group Policy Management Console (GPMC) .
- Create a new GPO named “Hardening Network Protocols” and link it to the Domain Controllers OU or the entire domain.
- Navigate to: Computer Configuration > Policies > Administrative Templates > Network > DNS Client.
- Enable the setting “Turn off multicast name resolution” . This disables LLMNR, preventing attackers from poisoning name resolution requests (Responder attacks).
3. Remote Management with RSAT and PowerShell
Managing AD directly on a Domain Controller is a bad practice (violating the “no source code on a live box” principle). Use Remote Server Administration Tools (RSAT) from a hardened admin workstation.
– Step-by-step guide (Installing RSAT on Windows 11):
1. Open PowerShell as an Administrator.
2. Install the AD module and management tools:
Get-WindowsCapability -Name RSAT.ActiveDirectory -Online | Add-WindowsCapability -Online
3. To query a user from your remote machine without RDPing to the DC:
Get-ADUser -Identity "jdoe" -Properties LastLogonDate, LockedOut -Server dc01.undercode.local
4. Cleaning Up Stale Objects and Inactive Accounts
Dormant accounts (stale users, old computer objects) are ticking time bombs. Attackers activate old accounts to blend in with legitimate traffic.
– Step-by-step guide (Finding and Disabling Stale Users):
1. Open PowerShell with the Active Directory module loaded.
2. Find users who haven’t logged on in 90 days:
$InactiveDate = (Get-Date).AddDays(-90)
Get-ADUser -Properties LastLogonDate -Filter {LastLogonDate -lt $InactiveDate -and Enabled -eq $true} | Select-Object Name, LastLogonDate, DistinguishedName
3. To disable them (after verifying):
Get-ADUser -Properties LastLogonDate -Filter {LastLogonDate -lt $InactiveDate -and Enabled -eq $true} | Disable-ADAccount
4. Linux (Cross-Platform): If using SSSD or PowerBroker Open, you can export the user list from AD using ldapsearch:
ldapsearch -x -H ldap://dc01.undercode.local -D "cn=admin,dc=undercode,dc=local" -W -b "dc=undercode,dc=local" "(lastlogon<=130000000000000000)" samaccountname
5. Implementing Monitoring for Security Anomalies
If you aren’t logging it, it didn’t happen. You need to monitor Event IDs specifically tied to AD compromise, such as Event ID 4769 (Kerberos ticket asking for privileged access) or 4776 (Credential Validation failures).
– Step-by-step guide (Configuring Advanced Audit Policy):
1. Open Group Policy Management Console.
- Navigate to Computer Configuration > Policies > Windows Settings > Security Settings > Advanced Audit Policy Configuration > Audit Policies.
- Enable Audit Kerberos Service Ticket Operations (Success and Failure) and Audit Logon (Success and Failure).
- Command to Search for “Golden Ticket” activity: Search the Domain Controller security log for Event ID 4769 with specific encryption types that are abnormal for your environment:
Get-EventLog -LogName Security -InstanceId 4769 -After (Get-Date).AddHours(-24) | Where-Object {$_.Message -match "Encryption Type: 0x17"} | Select-Object TimeGenerated, Message(Note: 0x17 indicates RC4 encryption, often used in pass-the-hash or Golden Ticket attacks).
6. Enforcing Password Policies and Fine-Grained Policies
Standard domain password policies are often too weak for admins and too strict for regular users.
– Step-by-step guide (Creating a Fine-Grained Password Policy):
1. Open Active Directory Administrative Center (ADAC) .
- Navigate to the System container > Password Settings Container.
3. Click New > Password Settings.
- Create a policy for Admins: Name
PSO_Admins, Precedence1, Minimum Password Length14, Complexity enabled. - Specify the “Applies to” group (e.g., “Domain Admins”).
6. PowerShell verification:
Get-ADFineGrainedPasswordPolicy -Filter 'Name -like "PSO_Admins"'
7. Disaster Recovery: The Authoritative Restore
Backing up AD is useless if you don’t practice the restore. Standard system state restores are non-authoritative; the restored DC will just re-sync the corrupted data from a healthy DC. If the corruption is widespread, you need an authoritative restore.
– Step-by-step guide (Command Line):
1. Reboot the Domain Controller into Directory Services Restore Mode (DSRM) .
2. Open Command Prompt and run `ntdsutil`.
3. At the `ntdsutil` prompt, type:
activate instance ntds authoritative restore restore subtree "OU=CriticalUsers,DC=undercode,DC=local"
4. This increments the version number of the objects in that OU, ensuring that when the DC reboots, it replicates its restored version to the other servers (overwriting the bad data), rather than the other way around.
What Undercode Say:
- The Domain Controller is the Kingdom’s Gate: The checklist provided is not just about IT hygiene; it is about preventing a single compromised workstation from granting the keys to the kingdom. Practices like disabling LLMNR and monitoring 4769 events are proactive measures against the specific TTPs used by Conti and LockBit affiliates.
- Automation is Non-Negotiable: Manually auditing users or permissions in a domain with thousands of objects is impossible. The commands provided (PowerShell for stale accounts, LDAP queries) must be scheduled and scripted. If you are not automating the discovery of inheritance breaks or inactive accounts, your environment is drifting into an unmanageable state daily.
Prediction:
As organizations continue their “cloud migration,” the on-prem Active Directory will increasingly become the “identity bridge” used to synchronize to Entra ID. Attackers are aware of this hybrid model. We predict a surge in attacks targeting the on-prem AD not to encrypt the local servers, but to poison the sync process, effectively taking over Office 365 and Azure environments through the backdoor of a poorly maintained Domain Controller. The checklist above will be the baseline defense required to prevent cloud breaches originating from legacy on-prem infrastructure.
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IT/Security Reporter URL:
Reported By: Bibek Adhikari – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
