Why do flat IT and OT networks increase cyber risk in utilities?

Why This Matters for Security Teams

Flat IT and OT networks remove the friction that security teams rely on to contain compromise. In utilities, that matters because historian servers, engineering workstations, remote access paths, and control assets often sit closer together than operators assume. Once an attacker lands on a business endpoint, lateral movement can quickly expose privileged services, proprietary process data, and systems that influence physical operations. Guidance in the NIST Cybersecurity Framework 2.0 emphasises asset visibility, protective safeguards, and recoverability, but those outcomes are much harder to achieve when the network does not create meaningful trust boundaries.

The risk is not only ransomware. Flat architectures also expand the blast radius for credential theft, supply chain compromise, remote maintenance abuse, and misuse of shared services. In OT environments, detection is often slower and response options are more constrained than in IT, so the attacker benefits from every internal hop that remains open. Current guidance suggests that utilities should treat segmentation as an operational resilience control, not just a network design preference. In practice, many security teams encounter OT exposure only after a business-side intrusion has already reached engineering assets, rather than through intentional zoning.

How It Works in Practice

Effective segmentation in utilities usually starts with defining zones around business IT, supervisory systems, engineering access, safety-related components, and vendor or remote support channels. The goal is not to isolate everything completely, but to make each pathway intentional, monitored, and limited to what the process requires. A flat network allows routable trust to become default trust; segmented design forces teams to specify who can reach what, from where, and under which conditions. That is the core idea behind NIST SP 800-207 Zero Trust Architecture, even though OT implementation must account for uptime, legacy protocols, and vendor dependencies.

In practice, utilities often combine VLANs, firewalls, jump hosts, industrial demilitarised zones, and strict remote access controls. The controls matter most at the boundary points where IT and OT exchange data, such as patch distribution, reporting, and historian replication. Monitoring also needs to follow the architecture. CISA advisory material frequently shows that attackers chain valid accounts, remote access tools, and exposed services once an internal foothold exists, so network boundaries should be paired with logging, alerting, and rapid isolation playbooks. The operational goal is to force compromise to stop at the first boundary rather than traverse the environment unchecked.

• Separate business IT, control, safety, and vendor access paths.
• Limit east-west traffic inside OT to explicit, documented use cases.
• Use jump servers or brokered access for administration instead of direct reachability.
• Monitor boundary traffic for unusual protocols, privilege use, and maintenance activity.
• Test restoration and segmentation bypass scenarios during exercises, not only during audits.

These controls tend to break down when legacy OT devices require broad broadcast visibility or when a utility still depends on direct vendor connectivity that has never been redesigned.

Common Variations and Edge Cases

Tighter segmentation often increases engineering overhead, so organisations have to balance containment benefits against uptime, maintenance complexity, and vendor support constraints. That tradeoff is especially sharp in older plants where devices cannot support modern authentication or where production systems were never designed for per-zone policy enforcement.

There is no universal standard for every OT topology, but best practice is evolving toward risk-based zoning rather than a single “air gap” assumption. Some utilities also need to preserve one-way data flows for reporting or telemetry, while others must allow tightly controlled remote maintenance windows. The important point is that each exception should be explicit, reviewed, and logged. Where AI-assisted monitoring is introduced, teams should also consider model and alert integrity, because the usefulness of detection depends on trustworthy inputs and decision paths. For adversarial AI considerations, MITRE ATLAS adversarial AI threat matrix is a useful reference point, and the Anthropic report on AI-orchestrated cyber espionage underscores how automation can accelerate reconnaissance once a flat environment is exposed.

For utilities, the practical decision is not whether to segment perfectly, but whether the design prevents a routine IT compromise from becoming a control-system event. Flat networks fail because they assume trust where operations actually require controlled separation.

Related resources from NHI Mgmt Group

• Why do shared VPNs and jump boxes increase lateral movement risk in OT networks?
• Why do legacy OT systems increase cyber risk in Industry 4.0 programmes?
• Why do flat networks increase risk in hospitals and other operational environments?
• Why do OT and IT integrations increase NHI risk?