The principle of least privilege (PoLP) means granting users, devices, and applications only the access they need — nothing more.
In industrial networks, this approach limits attack surfaces, prevents lateral movement, and helps meet compliance requirements such as CMMC, NIS2, and IEC 62443.

Many industrial assets were not designed with access control in mind.
PLCs, HMIs, and legacy engineering stations often run with default credentials or open communication paths.
Applying least privilege in these conditions requires controls that operate at the network level, not inside the endpoints.

In a typical OT network, once a user or service gains access, they can often reach every device on the same subnet.
A single compromised engineering laptop can affect production systems because communication paths are rarely restricted.

Least privilege addresses this by defining boundaries:

• Who can talk to each controller

• Which protocols are permitted

• When access is allowed

This approach aligns directly with compliance requirements:

• Access Control (AC) — Only authorized sessions are permitted.

• System and Communications Protection (SC) — Traffic follows defined and monitored paths.

• Audit and Accountability (AU) — Each access event is logged for review.

Least privilege is enforced through segmentation.
Segmentation limits communication between devices and users to what is required for operations.

Traditional VLANs and ACLs can achieve this but are difficult to scale or audit across industrial networks.
An alternative is to use software-defined enclaves — logical segments that define communication policy between devices without changing IP addressing or wiring.

Each enclave:

• Authenticates endpoints before communication.

• Restricts data paths to approved sources.

• Logs and inspects every session.

This turns network boundaries into policy enforcement points rather than static firewall rules.

Least privilege requires coordination between the teams responsible for connectivity and those responsible for operations.

Key steps:

• Maintain a shared inventory of devices and data flows.

• Classify assets by criticality and required communication paths.

• Define policies together — IT sets access rules, OT validates operational needs.

This collaboration ensures segmentation policies align with real production requirements and avoids blocking legitimate maintenance or data collection.

Remote maintenance is one of the main challenges for least privilege in OT.
Traditional VPNs provide network-wide access, which violates the principle by default.

Modern remote access solutions restrict each session to a single enclave or device.
Access is granted only when needed, with authentication tied to individual user identities and time limits.
Every action is recorded, creating verifiable audit evidence.

The Trout Access Gate applies least privilege through edge enforcement:

• Each device or group of assets is placed in an isolated enclave.

• Communication policies define which users or systems can connect.

• Remote sessions are authenticated and logged.

• No rewiring or reconfiguration of existing assets is required.

This model enforces least privilege across IT and OT networks while maintaining uptime and simplifying compliance audits.

Least privilege in industrial networks is achieved by controlling access paths, not by modifying legacy devices.
Segmentation, collaboration, and identity-based remote access make it possible to enforce precise policies that are both operationally safe and compliant.

With Trout Access Gate, these controls can be deployed incrementally — turning network policy into a measurable security improvement.