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Introduction:
For years, organizations have fallen into the trap of believing that deploying an Endpoint Detection and Response (EDR) tool equates to a bulletproof security posture. This mindset often leads to flat, poorly segmented networks where a single compromised credential can lead to total domain domination. The shift from reactive alert-monitoring to proactive architectural resilience requires a fundamental change: implementing robust administrative tiering models that contain breaches and protect critical assets, moving beyond the “I have an EDR, I’m secure” fallacy.
Learning Objectives:
- Understand the architectural flaws of flat networks and the principle of tiering models.
- Learn how to implement administrative tiering using Active Directory (AD) security groups and Privileged Access Workstations (PAWs).
- Gain hands-on skills in hardening network segmentation, configuring Windows Firewall rules, and monitoring tier violations.
You Should Know:
- The Anatomy of a Tiering Model: From Zero Trust to Active Directory Segmentation
A tiering model divides an IT environment into logical security layers based on the sensitivity of the assets. Typically, this is broken into Tier 0 (Domain Controllers, Identity Management), Tier 1 (Application Servers, Enterprise Servers), and Tier 2 (User Workstations, Employee Devices). The golden rule is that administrative accounts must never log into a lower tier than the one they manage.
To move from a flat network to a tiered architecture, start by discovering the current attack paths. Tools like BloodHound (SharpHound) are essential for visualizing how an attacker could move laterally.
Step-by-step guide to discovery and segmentation:
- Step 1: Map the Attack Paths. Run SharpHound on a domain-joined machine to collect data. Use the collector:
.\SharpHound.exe -c All --outputdirectory C:\temp\
Analyze the resulting JSON files in BloodHound to identify users who are local admins on Tier 0 machines (a critical violation).
- Step 2: Define Administrative Tiers. Create Organizational Units (OUs) for each tier in Active Directory Users and Computers (ADUC). Move high-value assets like Domain Controllers into a “Tier 0” OU.
- Step 3: Implement Privileged Access Workstations (PAWs). These are hardened, dedicated systems (often using Windows 10/11 Enterprise) used only for administrative tasks for specific tiers. Configure Group Policy Objects (GPOs) to restrict logon rights.
GPO Setting: Deny log on locally for non-Tier0 accounts on Domain Controllers Navigate to: Computer Configuration -> Policies -> Windows Settings -> Security Settings -> Local Policies -> User Rights Assignment Set "Deny log on locally" to include Tier1 Admins, Tier2 Admins, and Domain Users.
- Hardening the Gateway: Windows Firewall Rules for Tier Isolation
Once tiers are defined logically, you must enforce them at the network level. In a tiered model, Tier 0 (Domain Controllers) should only accept administrative traffic from Tier 0 PAWs. All other inbound traffic from lower tiers should be blocked unless absolutely required for business function.
Step-by-step guide to configuring Firewall rules:
- Step 1: Create a Security Group. In AD, create a global security group called
Tier0_Admin_Workstations. Add the computer accounts of your PAWs to this group. - Step 2: Implement Firewall Rules via GPO. On your Domain Controllers (Tier 0), create a GPO to filter inbound RPC, SMB, and WinRM traffic.
Using PowerShell to create a rule allowing WinRM only from Tier0 Workstations New-NetFirewallRule -DisplayName "Allow WinRM from Tier0" ` -Direction Inbound ` -Protocol TCP ` -LocalPort 5985 ` -RemoteAddress "192.168.10.0/24" ` IP range of Tier0 PAWs -Action Allow ` -Enabled True
Note: Ensure you create a deny rule for all other subnets before allowing this specific range to enforce isolation.
- Credential Hygiene: Removing Local Admin Rights and LAPS
A core pillar of tiering is preventing lateral movement. In flat networks, local administrator accounts often share the same password across thousands of machines. If an attacker cracks one, they have them all. Implementing the Local Administrator Password Solution (LAPS) is critical.
Step-by-step guide to deploying LAPS:
- Step 1: Extend the Schema. On the schema master, run `Update-AdmPwdADSchema` to add the necessary AD attributes.
- Step 2: Deploy the GPO. Apply the LAPS GPO to your workstations (Tier 2). Configure the policy to enable local admin password management and set complexity.
- Step 3: Audit. Use `Get-AdmPwdPassword` to verify passwords are unique and rotating.
Retrieve the LAPS password for a specific computer Get-AdmPwdPassword -ComputerName "WS-USER01"
Tiering Insight: Never use domain admin credentials to manage user workstations. Use delegated admin accounts that are restricted to Tier 2.
4. Monitoring Tier Violations: Sysmon and Event Logs
A tiering model is only as good as its enforcement. If a Tier 2 admin logs into a Domain Controller, the architecture has failed. Continuous monitoring for these “tier violations” is essential. Using Sysmon (System Monitor) and Windows Event Log forwarding, you can detect these anomalies in real-time.
Step-by-step guide to monitoring logon events:
- Step 1: Configure Sysmon. Deploy a Sysmon configuration that tracks network connections and process creation. Use SwiftOnSecurity’s open-source config as a baseline.
- Step 2: Monitor Event ID 4624. This event indicates a successful logon. Pay attention to `TargetUserName` and
WorkstationName.<!-- XML Query Example for Splunk/ELK to detect Tier 2 logging into Domain Controllers --> <Query> <Select Path="Security">[System[EventID=4624]] and [EventData[Data[@Name='TargetUserName']='Tier2_Admin']] and [EventData[Data[@Name='WorkstationName']!='PAW']]</Select> </Query>
- Step 3: Set Up Alerts. Configure your SIEM to trigger a critical alert when an account from a specific administrative group logs into a machine of a higher tier. For example, if a “Tier 2 Admins” group member logs into a Tier 0 server, generate an incident.
5. Linux Hardening in a Tiered Environment
Modern enterprises are hybrid. Tiering isn’t exclusive to Windows. For Linux servers (often Tier 1 or Tier 0 in identity infrastructure), strict sudoers policies and SSH key management are required.
Step-by-step guide for Linux tiering:
- Step 1: Restrict SSH Access. Edit `/etc/ssh/sshd_config` to restrict root login and define specific AllowGroups.
Restrict SSH to only users in the "tier1-admins" group AllowGroups tier1-admins PermitRootLogin no
- Step 2: Implement sudoers restrictions. Never give users full sudo access. Specify commands.
/etc/sudoers.d/tier1-admins %tier1-admins ALL=(ALL) /usr/bin/systemctl, /usr/bin/apt, !/usr/bin/passwd
- Step 3: Audit Sessions. Use `auditd` to track who does what on critical servers. Monitor for users running commands they shouldn’t.
6. API Security and Cloud Tiering (Azure AD)
As organizations migrate to the cloud, tiering must extend to Identity Providers (IdP) like Azure AD (Entra ID). Compromising a global administrator in Azure is the equivalent of owning the on-premises Tier 0. Implement Privileged Identity Management (PIM) to enforce Just-In-Time (JIT) access.
Step-by-step guide for cloud hardening:
- Step 1: Configure PIM. In Azure AD, enable PIM for Global Administrator and other privileged roles. Require approval and time-bound activation.
- Step 2: Conditional Access Policies. Enforce that privileged role activation can only occur from compliant devices (your Tier 0 PAWs) and require phishing-resistant MFA (like FIDO2 keys).
- Step 3: API Monitoring. Use the Microsoft Graph API to audit role assignments.
PowerShell to list active privileged role assignments in Azure AD Get-AzureADMSPrivilegedRoleAssignment -ProviderId AzureResources -Filter "isElevated eq true"
What Undercode Say:
- Key Takeaway 1: EDR is detection, tiering is containment. You cannot rely solely on an EDR to stop an attacker who has domain admin credentials; architectural segmentation is the only true barrier to a full domain compromise.
- Key Takeaway 2: Tiering fails without strict monitoring and enforcement. Implementing technical controls (GPOs, Firewalls, LAPS) is half the battle; continuous auditing for tier violations via Sysmon and SIEM alerts ensures that the model remains intact over time.
The analysis reveals that while technology is crucial, the human element remains the weakest link. Organizations often build perfect tiering architectures but fail to enforce them because “it’s easier” to give a developer local admin rights or to use a domain admin account for mundane tasks. The shift requires a cultural change, treating administrative credentials as the most valuable assets in the network.
Prediction:
As identity-based attacks continue to dominate the threat landscape (such as Golden Tickets, DCSync, and token theft), the adoption of strict tiering models will become a compliance requirement rather than a best practice. In the next two years, expect regulatory frameworks to mandate the segregation of administrative tiers, with audits focusing on lateral movement paths. The future of enterprise security lies not in finding a silver bullet product, but in architecting resilience through identity isolation and Zero Trust principles.
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