Why do flat networks increase risk in hospitals and other operational environments?

Flat networks let devices and systems communicate broadly by default, which makes lateral movement easier after one compromise. In a hospital, that can turn a single biomedical device or endpoint into a pivot toward other clinical or operational assets. The risk is not only breach propagation, but also disruption of patient care and recovery processes.

Why This Matters for Security Teams

Flat networks reduce the friction between systems, which is useful for uptime but dangerous for containment. Once a single endpoint, workstation, or biomedical asset is compromised, broad east-west reach can turn that foothold into a route across clinical, operational, and administrative systems. That matters in hospitals because patient care depends on availability, not just confidentiality, and disruptions can cascade quickly.

This risk is not limited to human users. Modern environments also rely on service accounts, integrations, and device identities, so network design and identity design overlap in practice. NHIMG’s Top 10 NHI Issues and Ultimate Guide to NHIs — Key Challenges and Risks both underline the same operational pattern: when identities are over-permissioned and visibility is weak, lateral movement becomes easier to sustain and harder to detect.

Current guidance from the NIST Cybersecurity Framework 2.0 treats segmentation and controlled access as core resilience measures, while NIST SP 800-207 Zero Trust Architecture shifts the default away from implicit trust. In practice, many security teams encounter the flat-network problem only after a ransomware event or device compromise has already made segmentation urgently necessary, rather than through planned architectural change.

How It Works in Practice

In a flat environment, a compromise rarely stays local. Attackers exploit one weak point, then enumerate nearby systems, reuse exposed credentials, and move toward higher-value targets such as domain services, imaging systems, or operational technology. The issue is not that every connection is malicious; it is that permissive pathways create too many choices once trust has been lost.

For hospitals and other operational environments, the practical failure mode is often a mix of legacy design, vendor support constraints, and uptime pressure. Many clinical or building systems were deployed to work reliably, not to enforce strong segmentation. As a result, teams may have IP-based allow lists in name only, with shared VLANs, broad administrative access, and limited monitoring of east-west traffic. That is exactly where identity governance becomes relevant. If service accounts, API keys, and device credentials are overbroad, the attacker can use legitimate access paths instead of noisy exploits.

Operationally, stronger containment usually means:

• Segmenting by function and criticality, not just by building or department.
• Separating clinical devices, user endpoints, servers, and administrative tooling.
• Using tight access policies for service accounts and device-to-device communications.
• Monitoring unusual east-west traffic, especially between segments that should rarely talk.
• Testing isolation paths before an incident, including manual recovery workflows.

That approach aligns with the 2024 ESG Report: Managing Non-Human Identities, which found that 72% of organisations have experienced or suspect a breach of non-human identities. The lesson is that broad connectivity plus weak identity hygiene creates a compound risk, not two separate ones. These controls tend to break down when legacy biomedical devices require vendor-specific reachability and teams leave exceptions in place indefinitely because patching or replacement windows are too disruptive.

Common Variations and Edge Cases

Tighter segmentation often increases operational overhead, requiring organisations to balance resilience against clinical continuity, vendor support, and maintenance complexity. That tradeoff is real: some devices cannot tolerate aggressive filtering, and some recovery processes depend on temporary broad access. Best practice is evolving toward compensating controls rather than pretending every asset can be isolated the same way.

For example, a radiology network, a laboratory environment, and a building-management system may each need different containment models. The right answer is usually not complete isolation everywhere, but risk-based segmentation with explicit exceptions, documented approvals, and periodic review. In environments with shared infrastructure, the goal is to stop lateral movement from becoming a default assumption.

This is also where NHI governance matters. If a device or application identity can reach more than it should, segmentation alone will not fully compensate. NHIMG’s Ultimate Guide to NHIs — Why NHI Security Matters Now is useful here because it ties weak credential discipline to real-world compromise paths. In other words, flat networks are dangerous not only because they connect systems, but because they amplify every mistake in identity, privilege, and recovery design.

Related resources from NHI Mgmt Group

• Why do shared device keys increase operational risk in OT environments?
• Why do SSO environments increase the risk of lateral movement?
• Why do layoffs increase insider-risk exposure in SaaS environments?
• Why do cloud environments increase non-human identity risk?