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Introduction:
Modern enterprise networks often suffer from a fundamental architectural flaw: flatness. In a flat network, a compromised workstation can serve as a beachhead for attackers to move laterally, exploiting trust relationships until they seize control of the entire Active Directory (AD) domain. The solution lies in tiering models—a strategic segmentation of administrative privileges and systems that creates impassable barriers between different levels of security sensitivity.
Learning Objectives:
- Understand the security risks inherent in flat enterprise network architectures.
- Learn how Active Directory tiering models (Tier 0, 1, 2) contain lateral movement and privilege escalation.
- Acquire practical commands and configurations to implement tiering boundaries on Windows and Linux administrative systems.
You Should Know:
- Deconstructing the Flat Network: Why Lateral Movement Succeeds
In a flat network, there is no logical separation between high-value assets (domain controllers) and standard user workstations. A single compromised user account with local admin rights can often be used to harvest credentials (like NTLM hashes) from memory, enabling pass-the-hash attacks that grant access to servers and ultimately domain controllers. This lack of segmentation means that an attacker moving from workstation to server is not crossing a security boundary—they are simply traversing an open plane.
To visualize this, consider the network from an attacker’s perspective. Using tools like BloodHound or SharpHound, they map AD relationships. If the helpdesk staff (who have local admin rights on workstations) are also domain admins, the path to complete compromise is short. The tiering model disrupts this by forcing attackers to bypass administrative controls that are physically or logically isolated.
- Implementing the Microsoft ESAE (Red Forest) and Tiering Model
Microsoft’s Enhanced Security Administrative Environment (ESAE), often called the “Red Forest,” or the simpler Tier 0/1/2 model, creates distinct administrative tiers:
– Tier 0: Domain controllers, PKI infrastructure, and identity management systems. Accounts in this tier cannot log into lower-tier systems.
– Tier 1: Enterprise servers (file servers, email, applications).
– Tier 2: User workstations and devices.
Step‑by‑step guide: Verifying and Enforcing Tier Boundaries
To enforce these boundaries, administrators must ensure that Tier 0 accounts never authenticate to Tier 2 machines. This is enforced via Group Policy and authentication policies.
On a Domain Controller (Windows Server):
Use PowerShell to configure Authentication Policies and Silos. This prevents high-value accounts from logging onto lower-tier machines.
Create an Authentication Policy for Tier 0 Admins New-ADAuthenticationPolicy -Name "Tier0_Policy" -UserTGCLimit 4 -ProtectedAccounts $true Create an Authentication Policy Silo and add the Tier0 Admin group New-ADAuthenticationPolicySilo -Name "Tier0_Silo" -AuthenticationPolicy "Tier0_Policy" -ComputerAuthPolicy "Tier0_Policy" -ServiceAuthPolicy "Tier0_Policy" -Enforced $true Add the Tier0 administrators group to the silo Set-ADGroup -Identity "Domain Admins" -AuthenticationPolicySilo "Tier0_Silo"
This configuration ensures that if a Domain Admin attempts to log into a standard workstation (Tier 2), the authentication fails.
On a Linux Jump Server (Tier 1 Bastion):
For environments managing Linux servers within the tier model, bastion hosts serve as hardened jump points. Configure `sshd` to restrict access based on groups and enforce multi-factor authentication (MFA).
Edit /etc/ssh/sshd_config to restrict Tier1 admins AllowGroups tier1_admins AuthenticationMethods publickey,keyboard-interactive Restart service sudo systemctl restart sshd
3. Hardening Active Directory with Administrative Tiering
Beyond authentication silos, technical controls must be applied to prevent “over-privileged” users. A common mistake is allowing standard IT support accounts to have local admin rights on workstations and server admin rights on domain controllers simultaneously.
Step‑by‑step guide: Implementing Local Admin Restrictions via Group Policy
1. Create Group Policy Objects (GPOs): Separate GPOs for each tier.
2. Restrict Local Administrators Group: Use Restricted Groups or Group Policy Preferences to define who is a local admin on workstations. Ensure that only designated Tier 2 admin accounts (not Tier 0) are in the local administrators group on endpoints.
3. Apply Windows Firewall Rules: To prevent lateral movement protocols like SMB (port 445) or RPC (port 135) from crossing tiers, configure advanced firewall rules.
– Block SMB from Tier 2 to Tier 0: On the Tier 0 network segment, create an inbound rule to block all traffic from IP ranges designated for Tier 2 workstations.
Command to list all members of the local Administrators group (Windows):
net localgroup Administrators
Regular audits should ensure no Tier 0 accounts appear in the output on workstations.
- Monitoring for Tier Violations with Sysmon and SIEM
Even with controls in place, misconfigurations or temporary exceptions can occur. Continuous monitoring is essential. Sysmon (System Monitor) on Windows can log network connections and process creation, which is invaluable for detecting cross-tier authentication attempts.
Step‑by‑step guide: Deploying Sysmon to Detect Tier Crossings
1. Download Sysmon from Microsoft Sysinternals.
- Create a configuration file (e.g.,
sysmon-config.xml) that logs network connections (Event ID 3) and specifically flags connections to Domain Controllers from non-privileged source IPs.
3. Install Sysmon:
sysmon -accepteula -i sysmon-config.xml
4. Forward logs to a SIEM (e.g., Splunk, Sentinel) and create alerts for:
– Event ID 4624: An account logon where the account is a Tier 0 member but the workstation is in the Tier 2 OU.
– Event ID 4672: Special privileges assigned to a new logon (indicating admin usage).
For Linux, use `auditd` to track sudo usage and SSH logins from accounts that should be confined to specific tiers.
Audit all sudo commands to a specific file echo "-w /var/log/sudo.log -p wa -k sudo_audit" >> /etc/audit/rules.d/audit.rules auditctl -R /etc/audit/rules.d/audit.rules
- API Security and Cloud Hardening in Hybrid Environments
Tiering is not exclusive to on-premises Active Directory. In hybrid environments (Azure AD / Entra ID), the same principles apply. Privileged Identity Management (PIM) acts as the tiering control for the cloud.
Step‑by‑step guide: Configuring Entra ID Privileged Identity Management (PIM)
1. Navigate to Entra ID > Identity Governance > Privileged Identity Management.
2. For any administrative role (e.g., Global Administrator, Exchange Administrator), configure settings:
– Require MFA: Enforce Azure AD MFA on activation.
– Require Approval: Require a separate approver for activation.
– Activation Duration: Set to a maximum of 8 hours.
3. Just-In-Time (JIT) Access: Ensure no permanent assignment of high-tier roles. Users must activate the role to perform admin tasks, reducing the standing privileges that attackers could steal.
API Security Consideration:
When securing APIs in a cloud environment, apply the same tier logic. Critical infrastructure APIs (Tier 0) should not accept tokens generated for applications running on standard compute instances (Tier 2). Use Azure Policy or AWS IAM to enforce that only managed identities from specific, secured subnets can authenticate to the control plane API.
6. Vulnerability Exploitation and Mitigation: The Tiering Shield
Flat networks often exacerbate vulnerabilities like PrintNightmare (CVE-2021-34527) or Zerologon (CVE-2020-1472) . In a flat network, an exploit on a user workstation could be leveraged to target domain controllers directly over network protocols. Tiering mitigates this by placing network segmentation (firewalls or VLAN ACLs) between workstation subnets and server subnets.
Mitigation Commands:
- Windows Firewall Command (as Admin) to block inbound SMB from a specific subnet:
New-NetFirewallRule -DisplayName "Block SMB from Tier2" -Direction Inbound -Protocol TCP -LocalPort 445 -RemoteAddress 192.168.2.0/24 -Action Block
- Linux IPTables to block access to domain controller:
iptables -A INPUT -s 192.168.2.0/24 -d 10.0.0.10 -p tcp --dport 445 -j DROP
These commands physically prevent network communication, acting as a last line of defense even if administrative policies fail.
What Undercode Say:
- Security Architecture is Deterministic: Relying solely on user awareness or software patches is insufficient. A deterministic model like tiering, enforced by network controls and authentication policies, mathematically reduces the attack surface.
- Operational Discipline is Key: Tiering models fail when administrators “break glass” for convenience. Continuous monitoring for tier violations is as critical as the initial implementation.
Tiering models transform Active Directory from a sprawling, interconnected identity system into a hardened enclave of privileged operations. By combining Microsoft’s ESAE principles with strict network segmentation, API security policies, and relentless monitoring, enterprises can effectively nullify the “lateral movement” phase of an attack. The goal is to ensure that compromising a single workstation never leads to the kingdom of domain administration. While attackers will always find new exploits, a properly tiered network forces them to achieve multiple, distinct breakthroughs—increasing detection probability and slowing their progress to a crawl.
Prediction:
As hybrid work and cloud-native identities (Entra ID, AWS IAM) converge with on-premises AD, tiering models will evolve into unified “identity fabric” segmentation. We predict that within three years, regulatory frameworks (like PCI-DSS and NIS2) will explicitly mandate administrative tiering as a baseline requirement, moving it from a “best practice” to a “compliance necessity.” Automation tools like Terraform and Azure Policy will become the primary enforcement mechanisms for tiering in cloud environments, replacing manual Group Policy management.
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Reported By: Abelousova Breaking – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
