Designing a Tier 0 Privileged Access Model That Works Across Environments

After implementing this in dozens of environments, here's the reusable framework I keep coming back to:

Start with the definition, not the technology

Tier 0 = anything that can directly or transitively control your identity fabric. Domain Controllers, Entra Connect servers, ADFS, PKI, your PAM solution, backups of all the above, and any tool with SYSTEM-level agents on those assets (yes, that often means your EDR and SCCM).

The 5 design principles that always apply

1. Clean Source: A higher tier never trusts or depends on a lower tier. Your DC should never be managed from a workstation that browses the web.

2. Credential Isolation: Tier 0 admin accounts never authenticate to Tier 1 or 2 systems. Period. Use dedicated accounts (e.g. `t0-jdoe`) with no mailbox, no SSO into productivity apps.

3. Privileged Access Workstations (PAWs) :Hardened, dedicated devices for Tier 0 work. No email, no browsing, no Teams. Locked-down image, allow-listed apps, separate update path.

4. Just-in-Time Acces : Standing privilege is dead. Use PIM/PAM with approval workflows, time-bound elevation, and full session recording.

5. Authentication Policies & Silo— Enforce isolation at the Kerberos level so Tier 0 credentials physically cannot be used outside Tier 0 — even if stolen.

Why this framework is reusable

The principles are technology-agnostic. Only the implementation changes:

On-prem AD :Authentication Policy Silos, Protected Users group, Red Forest / ESAE patterns where justified

1. Hybrid :Cloud Kerberos Trust, hardened Entra Connect, separate cloud-only break-glass accounts

2. Cloud-first Conditional Access targeting privileged roles, Entra PIM with approval, restricted management groups, Privileged Identity Workstations

The mistakes I still see in almost every assessment:

• Backup admins forgotten: they can restore your DCs, so they're Tier 0

• EDR / AV consoles classified as Tier 1, even though they have SYSTEM on every DC

• Vulnerability scanners running with Domain Admin

• Service accounts crossing tiers "just temporarily" for 6 years

• No separate break-glass accounts, or break-glass stored in the same vault that depends on AD

The order that works: inventory → classify → isolate → automate with PAM → monitor

#CyberSecurity #ActiveDirectory #IdentityAndAccessManagement #PrivilegedAccess #ZeroTrust #InfoSec