Why do machine identities create risk in industrial networks when discovery and control are incomplete?

Machine identities become risky when teams cannot see all assets, connections, and protocols involved in production workflows. Hidden or unmanaged machine-to-machine access creates blind spots, weakens least privilege, and makes it harder to detect unauthorized communication. In practice, incomplete discovery turns identity governance into a partial control rather than an enforceable security boundary.

Why This Matters for Security Teams

Industrial networks depend on machine-to-machine trust that often predates modern security controls. When discovery is incomplete, service accounts, API keys, device certificates, and embedded credentials can keep operating without a clear owner, a known purpose, or a defined expiry. That creates a structural gap: security teams cannot reliably answer what exists, where it communicates, or whether the access still matches production need. NIST’s Cybersecurity Framework 2.0 treats visibility and governance as prerequisites for effective risk management, but industrial environments often have legacy protocols and segmented operations that make that prerequisite hard to meet.

NHIMG research shows why this matters: only 5.7% of organisations report full visibility into their service accounts in the Ultimate Guide to NHIs — Key Challenges and Risks. In a plant or OT-adjacent environment, that blind spot can turn a routine machine identity into an uncontrolled pathway between systems, vendors, and production tiers. In practice, many security teams encounter unauthorized machine access only after it has already been used to move laterally through a production workflow, rather than through intentional discovery.

How It Works in Practice

Incomplete discovery makes machine identity risk difficult to contain because industrial access paths are often distributed across controllers, historians, engineering workstations, broker services, and remote support tools. A single workflow may rely on multiple identities, each with different protocol expectations and privilege levels. If one of those identities is never inventoried, its access can persist unnoticed long after the original deployment or vendor integration.

Practitioners should think in terms of three linked controls: inventory, authorization, and revocation. First, discover identities and map them to assets, owners, and protocols. Second, validate that each identity only has the minimum access needed for the task, using policy rules aligned to NIST SP 800-53 Rev 5 Security and Privacy Controls. Third, tie every credential to a lifecycle process so it can be rotated or revoked when equipment is retired, reimaged, or reconfigured. NHIMG’s NHI Lifecycle Management Guide is clear that unmanaged offboarding is one of the most common ways machine identity risk persists.

• Map machine identities to specific industrial functions, not just to servers or vendors.
• Track protocol-level communication, including east-west traffic that may bypass normal perimeter tools.
• Use short-lived credentials where operationally feasible, especially for temporary maintenance and integration tasks.
• Review third-party and remote-access identities separately, since they often have broader reach than internal accounts.

For industrial control systems, the challenge is not only finding identities, but proving which ones are still active in a live process. These controls tend to break down when legacy OT assets cannot support modern logging, certificate rotation, or real-time policy enforcement because the operational process depends on static credentials and uninterrupted uptime.

Common Variations and Edge Cases

Tighter discovery and control often increases operational overhead, requiring organisations to balance stronger visibility against maintenance windows, vendor dependencies, and safety constraints. That tradeoff is especially sharp in OT environments where protocol support is limited and changes can affect availability.

Best practice is evolving for environments with unmanaged legacy assets. There is no universal standard for full machine-identity enforcement in industrial networks yet, so many teams use a phased approach: start with passive discovery, then classify identities by criticality, then enforce stronger controls on the highest-risk pathways. The NIST SP 800-207 Zero Trust Architecture model is useful here, but it must be adapted for OT realities where some assets cannot support continuous reauthentication.

Edge cases also include vendor-managed remote support, shared service credentials, and embedded device certificates that cannot be easily rotated without coordinated downtime. In those situations, current guidance suggests compensating controls such as network segmentation, strict session monitoring, and explicit approval workflows while a safer identity model is introduced. NHIMG’s Top 10 NHI Issues is a useful reference point for prioritising the identities most likely to remain hidden and over-privileged.

Where organisations fail most often is assuming that a machine identity is low risk because it is not interactive, when in reality it may be the most persistent and least visible access path in the environment.

Related resources from NHI Mgmt Group

• Why do non-human identities create more audit risk than human accounts?
• Why do non-human identities create audit risk in modern environments?
• Why do non-human identities create compliance risk even when policies exist?
• Why do machine identities create more operational risk when ownership and inventory are incomplete?