The FBI’s warning about criminal exploitation of unsecured VPNs landed hard in industrial circles—and for good reason. Remote access is a daily operational necessity in OT environments, yet it remains one of the most common entry points attackers use to reach control systems. Securing remote access in OT environments requires strategies built around how industrial operations actually work, not adapted from enterprise IT playbooks.
Why OT Remote Access Is a Different Problem
Industrial operators depend on remote access for maintenance, vendor support, and real-time monitoring. But the risks look nothing like enterprise IT. OT systems prioritize availability and safety above all else. A misconfigured remote access solution can halt production, introduce unsafe process states, or expose legacy systems that were never designed to be internet-adjacent.
Consider a typical OT environment: PLCs and RTUs running Modbus or DNP3, limited bandwidth, and systems that can only be updated during narrow maintenance windows scheduled weeks in advance. Standard IT controls—aggressive scanning, continuous patching, endpoint agents—are often unsafe to apply directly. Security controls must be designed around operational realities, not imposed on top of them.
Start With What You Can See: Asset Visibility
Securing remote access begins with knowing what is on the network. Without an accurate, current inventory of OT assets, access policies are built on guesswork. Asset visibility means tracking devices, firmware versions, communication patterns, and configuration states in near-real time—so that unauthorized connections or changes to control logic surface quickly rather than going undetected for months.
A plant running hundreds of field devices across segmented zones needs that inventory to enforce meaningful access controls. If you do not know which assets exist, you cannot define who should reach them or flag when something unexpected does. OT asset visibility is the foundation every security program builds on—remote access policy is no exception.
Protocol-Aware Controls for Industrial Networks
OT networks use industrial protocols—OPC UA, Modbus TCP, DNP3, EtherNet/IP—that standard enterprise firewalls often cannot inspect meaningfully. Deploying controls that are blind to these protocols creates false confidence. A firewall that passes all traffic on port 502 because it cannot parse Modbus function codes is not providing the protection it appears to.
Protocol-aware firewalls and deep-packet inspection tools designed for OT can enforce least-privilege communication rules at the process level. Paired with network segmentation—dividing the environment into zones such as process control, SCADA, and engineering workstations—these controls limit the blast radius of any single compromised remote session. Segmentation is not a one-time project; it requires ongoing validation as the network evolves and new vendor connections are added.
For practical guidance on how OT security assessments can identify remote access gaps without disrupting production, the evaluation process itself should mirror the operational care expected of any control you deploy.
Zero Trust Principles Adapted for OT
Zero Trust—never trust, always verify—is a sound architectural direction for OT remote access, but it must be adapted to industrial constraints. Implementing multi-factor authentication for all remote sessions is achievable in most environments and eliminates credential-only access as a viable attack path. Least-privilege access controls ensure that a vendor connecting to service one PLC cannot browse the rest of the network.
The adaptation piece matters. Session timeouts, jump servers, and role-based access rules all need to account for the reality that a technician mid-procedure cannot be locked out without consequence. Access policies should be designed with input from operations staff, not written in isolation by IT or security teams. This is where the principle of security built into operations—rather than layered on top—becomes concrete.
Testing OT remote access paths without touching live systems is one way to validate that these controls work as intended before an attacker finds the gaps first.
Behavioral Baselines Reduce Noise and Catch Real Threats
Once access controls are in place, monitoring remote sessions against behavioral baselines is what turns detection into something actionable. OT networks are relatively predictable—the same devices communicating with the same peers, following the same timing patterns day after day. Anomalies stand out when you have an established baseline to compare against.
The critical nuance is human context. A change in control logic during a planned commissioning activity should not trigger a response escalation. A vendor connecting from an unexpected geography at 2 a.m. should. OT analysts need enough operational familiarity to make that call reliably. This is why monitoring in OT is not simply a technology deployment—it requires people who understand both the security signals and the process context behind them.
Logging remote access sessions, capturing connection metadata, and retaining evidence also supports compliance obligations. NIST SP 800-82 provides detailed guidance on securing industrial control system environments, including remote access architectures appropriate for OT. Standards such as IEC 62443 and NERC CIP mandate access controls, logging, and incident response readiness—requirements that a well-instrumented remote access program can satisfy without significant additional overhead.
Compliance as a Design Input, Not an Afterthought
NERC CIP and IEC 62443 are not checkbox exercises for industrial operators in regulated sectors—they define minimum expectations for how remote access must be managed, logged, and audited. Building compliance requirements into the remote access architecture from the start is far less disruptive than retrofitting controls after the fact.
For example, NERC CIP requires logged evidence of all remote access to Electronic Security Perimeters. Deploying a jump server with session recording satisfies this requirement and gives operations a searchable record of what any vendor or employee did during a remote session. IEC 62443 zone-and-conduit models map directly to the segmentation strategies described above. Aligning to these frameworks is not about regulatory burden—it is about building a program that holds up under scrutiny and scales as the environment grows.
Building Security Into Remote Access, Not Bolting It On
The FBI’s VPN warning is a useful forcing function, but the underlying problem predates any single advisory. Remote access in OT environments has been under-secured for years because the controls available were either designed for IT or too disruptive to deploy without operational risk. That gap has narrowed considerably as OT-native security tools have matured.
The path forward is not to restrict remote access—it is to make it accountable. Asset visibility, protocol-aware segmentation, Zero Trust access controls, behavioral monitoring, and compliance alignment are not independent projects. They form a coherent program when designed together with operations in mind. That is the difference between security imposed on an industrial environment and security built into it.
If the FBI’s warning prompted a conversation in your organization about whether your remote access architecture would hold up, that conversation is worth continuing. Red Trident’s team works with industrial operators to assess remote access exposure, close gaps, and build monitoring capable of catching what policies alone cannot prevent. Contact Red Trident to discuss your OT remote access security posture.
