Why do non-human identities increase risk in OT environments?

Why Non-Human Identities Increase Risk in OT Environments

OT environments are especially sensitive to non-human identities because they often bridge production systems, vendor support paths, maintenance workflows, and remote administration. When a service account, API key, or machine credential is overprivileged or left unattended, it can become a durable path into critical systems long after the original purpose has ended. NHI Management Group research shows that 80% of identity breaches involved compromised non-human identities such as service accounts and API keys, which is especially relevant when those identities touch control systems or engineering workstations.

In OT, the risk is not only compromise but persistence. Credentials used for patching, telemetry, historian access, or third-party support can survive staff changes, project completion, and even segmentation changes if lifecycle controls are weak. That creates exposure across both IT and operational boundaries, where the blast radius can include safety, availability, and process integrity. Guidance from the NIST Cybersecurity Framework 2.0 reinforces that governance must cover assets, access, and recovery together, not as separate silos. In practice, many OT teams only discover NHI sprawl after a maintenance credential is reused in a place no one expected.

For broader context on how identity sprawl accumulates, see Ultimate Guide to NHIs — Why NHI Security Matters Now and Top 10 NHI Issues.

How That Risk Shows Up in Practice

OT risk increases when machine identities are granted broad access to systems that were never designed for modern identity governance. A vendor VPN account may authenticate a remote support tool, which then reaches a jump host, which then opens a pathway to an HMI, historian, or controller management plane. If each step uses a static credential, incident responders inherit a chain of trust that is hard to inspect and harder to revoke. The practical goal is to treat each non-human identity as a bounded workload identity, not as a convenience account.

Current guidance suggests three controls matter most: ownership, scope, and expiry. Ownership means every NHI has a named business and technical owner. Scope means the credential only reaches the specific device, protocol, or service required. Expiry means the credential is short-lived or rotated automatically, especially for remote access, automation, and third-party integrations. Where possible, use secrets managers, just-in-time issuance, and policy-as-code so access can be evaluated at request time instead of encoded permanently into scripts or shared accounts. This aligns with the operational direction of Ultimate Guide to NHIs — Key Challenges and Risks and the OWASP NHI Top 10, which both emphasise credential lifecycle discipline and least privilege.

• Map each NHI to a specific OT use case, such as patching, telemetry, or vendor support.
• Separate human access from machine access so shared accounts do not mask accountability.
• Prefer short-lived credentials and automate revocation when the task ends.
• Log credential use with enough context to trace lateral movement across sites and zones.

These controls tend to break down in brownfield OT environments where legacy devices cannot support modern authentication, because operators then fall back to shared passwords and exception-based access.

Common OT Edge Cases and Tradeoffs

Tighter identity control in OT often increases operational overhead, requiring organisations to balance resilience against uptime constraints. Legacy PLCs, air-gapped segments, and vendor-managed systems may not support per-session authentication or modern token exchange, so current guidance suggests compensating controls rather than forcing a one-size-fits-all model. In those cases, segmentation, protocol allowlisting, jump servers, and tightly monitored break-glass accounts become essential guardrails.

There is also a difference between routine automation and emergency access. A backup script that runs every hour is not the same as a vendor account used once during a plant outage, but both can become risky if they are treated as permanent. Best practice is evolving toward explicit exception handling: document why the NHI exists, who approves it, when it expires, and how it is reviewed after the event. For organisations looking to benchmark maturity, NHI Management Group notes that only a minority have formal offboarding processes for API keys, which is a warning sign in environments where downtime pressure can easily override governance. If an OT identity cannot be shortened, scoped, or monitored, it should be treated as an exception with compensating controls, not as a normal account.

Related resources from NHI Mgmt Group

• Why do non-human identities create audit risk in modern environments?
• Why do non-human identities create more audit risk than human accounts?
• How should security teams govern non-human identities in cloud environments?
• Why do non-human identities create compliance risk even when policies exist?