In early 2024, the Ann & Robert H. Lurie Children’s Hospital of Chicago faced a catastrophic cyber incident. Between January 26 and 31, attackers infiltrated the network, forcing the shutdown of phones, email, and critical patient systems including the EHR and online portal. Nearly 800,000 individuals were later notified that their personal and medical data had been compromised. While the precise attack vector was not confirmed, the episode illustrates how outdated identity infrastructure, especially legacy on-premises Microsoft Active Directory (AD) installations, can become the Achilles’ heel of healthcare IT.
The Legacy Infrastructure Risk
Hospitals and healthcare systems operate some of the most complex IT estates imaginable. Decades of deployed applications, frequent mergers and acquisitions (M&As), specialist medical systems, and embedded devices that rely on outdated operating systems have created a web of dependencies. Within that mix, it is common for an old AD domain controller to remain online solely to support a legacy or niche application. These forgotten servers often escape patching, monitoring, and lifecycle management.
Once a neglected domain controller is left connected, it becomes a hidden doorway into the hospital’s identity layer. Attackers who gain an initial foothold through phishing, remote access, or insecure endpoints, can target AD to escalate privileges, move laterally, and deploy ransomware. Because AD functions as the keys to the kingdom in Windows environments, compromising a privileged object or domain controller often equates to full network control.
Although Lurie Children’s did not disclose that AD was involved, the extensive shutdown, breadth of data exposure, and prolonged recovery imply a serious identity-level compromise – resulting in severe financial and operational consequences.
Poor AD Hygiene and Oversight
Active Directory hygiene is frequently inadequate in healthcare. Legacy service accounts, disabled or stale user accounts, and built-in AD groups such as Backup Operators or Account Operators often remain active with elevated privileges and little oversight, giving attackers easy avenues for escalation.
Many hospitals still rely on outdated authentication protocols or weak Kerberos configurations to maintain compatibility with legacy systems. These older protocols create weaker cryptographic paths that can be exploited for credential theft. Domain controllers themselves are often unpatched or outdated, particularly those kept online to support single-purpose or legacy applications. Once compromised, they give adversaries complete control of user access and credential stores.
Frequent M&As further complicate matters. Each merger introduces new forests, domains, and legacy trusts, creating sprawling, inconsistent identity environments. Under pressure to integrate clinical systems quickly, IT teams often postpone identity consolidation and decommissioning work indefinitely.
Meanwhile, audit logging, privileged-account monitoring, and identity threat detection remain underfunded. Hospitals understandably prioritise clinical technologies over infrastructure investment, but this imbalance leaves AD largely unguarded. A single compromised account or domain controller can therefore trigger a hospital-wide crisis, disrupting operations and exposing patient data.
Why AD Is a Prime Target for Ransomware
Attackers increasingly view identity infrastructure as the most efficient way to gain dominance within a network. A compromised domain controller lets them move laterally at speed, harvest credentials, escalate privileges, and push ransomware across systems, all from the core of the organisation’s trust fabric.
Active Directory’s architecture magnifies the risk. Because replication automatically distributes changes throughout the forest, a single malicious action, such as the creation of a rogue administrator account or the alteration of a group policy, can spread instantly.
Historic vulnerabilities like Zerologon have shown how flaws in domain controller protocols can allow attackers to impersonate controllers and seize domain-admin privileges. Even after such exploits are patched, legacy or poorly maintained servers often remain exposed, giving adversaries continued opportunity.
Once AD is breached, the consequences are wide-ranging. Ransomware operators can encrypt endpoints and file shares, disable or corrupt backups, and exfiltrate sensitive data before encryption. What follows is the often used double-extortion playbook, involving lock out and threats of public release. A hospital’s legacy AD with weak hygiene is a high-value target and an inviting entry point for ransomware.
Practical Steps to Protect Active Directory
To reduce ransomware risk, hospitals must take a proactive, identity-first approach. Start by auditing all domain controllers and legacy domains to identify outdated or redundant systems, then patch, update, or retire them. Following M&As or system integrations, review and eliminate obsolete trusts to shrink the attack surface.
Security must also extend to configuration and privilege management. Enforce least privilege by removing unnecessary admin rights, disable legacy authentication protocols, and review permissions regularly. Continuous monitoring and periodic health checks help uncover misconfigurations, stale accounts, and suspicious activity before attackers can exploit them. Domain controllers should be tightly segmented, with restricted access and no additional workloads hosted on them.
Hospitals should also maintain and test a recovery plan to restore AD quickly if compromised. Identity hygiene should be treated as a core pillar of operational resilience and not as a secondary IT task.
The Time for Hospitals to Act Is Now
The Ann & Robert H. Lurie Children’s Hospital incident demonstrated the opportunity, scale and impact of the threat within a healthcare environment. Cybercriminals now see healthcare as a soft target, where mission-critical operations, fragmented IT environments, and outdated identity systems combine to create ideal conditions for attack.
Hospitals burdened by years of technical debt can no longer treat identity infrastructure as an afterthought. With risks at an all-time high, organizations must move from reactive cybersecurity to proactive identity resilience. When an outdated AD domain controller stays online just to support a single legacy application, it leaves the entire hospital only one phishing click away from a full-scale ransomware disaster.
Every ransomware outbreak reinforces the same lesson. That is, the weakest link is often a forgotten system that no one owns. In healthcare, that link is frequently a legacy AD controller still tied to an obsolete application. Securing identity isn’t just good cyber hygiene, it’s vital to protecting patients, safeguarding data, and keeping hospitals operational when it matters most.
About Craig Birch
Craig Birch is a Technology Evangelist/Principal Security Engineer at Cayosoft. With over 25 years of experience, his mission is to teach organizations about Active Directory and Entra ID security to keep the bad actors out
