CIO Brief: Hybrid Identity Means On-Prem Flaws Become Cloud Flaws
Retrospective: this article looks back at events from September 2020, written in 2026 with the benefit of hindsight.
The short version: In 2020, a flaw called Zerologon let attackers take over a company's core identity system — Active Directory — in seconds, without a password. Because most companies connect that system to Microsoft 365, an on-premises flaw can become a cloud breach.
Why hybrid identity matters to leadership
Most mid-sized organizations still run Active Directory on their own servers and synchronize it to Microsoft's cloud. That makes sign-in convenient, but it ties the security of your cloud to the security of older on-premises systems. A weakness in either can compromise both.
The business impact
- Company-wide compromise if Active Directory falls.
- Cloud exposure through synchronized accounts and identity servers.
- Long recovery — rebuilding identity infrastructure takes weeks.
Questions to ask your team
- How quickly are critical patches applied to our domain controllers?
- Are we monitoring Active Directory for attacks?
- Which cloud administrator accounts are synchronized from on-premises, and could an on-prem attacker take them over?
- Do we have a plan to reduce our dependence on on-premises identity?
What good looks like
Domain controllers patched within days, monitored continuously, cloud administrators using cloud-only accounts, and a roadmap to reduce on-premises identity dependencies.
The decision
Ask for confirmation that no cloud administrator account is synchronized from on-premises Active Directory. It's a simple separation that limits how far an on-prem breach can reach.
- Zerologon (Aug–Sept 2020): Taking Over a Domain Controller in Seconds Incident Teardowns
- How to Patch and Monitor Domain Controllers in Hybrid Azure Environments How-To & Hardening
- Detecting Netlogon Exploitation: Defender for Cloud and Sentinel KQL Detection & Response