Top 10 Zero-Trust Solutions for OT Environments 

The New Industrial Reality: Why Zero Trust is Non-Negotiable for OT

For decades, Operational Technology (OT) and Industrial Control Systems (ICS) have relied on a security model best described as a hard shell with a soft center: the network perimeter. The implicit assumption was, “If it’s inside the firewall, it can be trusted.” This model, based on air-gapped or heavily segmented networks (like the Purdue Model), is rapidly becoming obsolete.

Today’s industrial landscape is defined by the convergence of IT and OT (IT/OT convergence), the rise of Industry 4.0, and a surge in remote access for maintenance, operations, and third-party vendors. This connectivity, while driving efficiency, has shattered the illusion of the secure perimeter. The result? A widening attack surface that nation-state actors and sophisticated cybercriminals are actively exploiting for reconnaissance, persistence, and potential catastrophic disruption of critical infrastructure-from energy grids and manufacturing plants to water treatment facilities.

The answer to this evolving, persistent threat is the Zero Trust Architecture (ZTA).

What is Zero Trust in the Context of OT/ICS?

The foundational mantra of Zero Trust is “Never Trust, Always Verify, Enforce Least Privilege, and Assume Breach.”

In a traditional IT environment, this means eliminating implicit trust for users and devices, even if they are on the corporate network. For the complex, safety-critical world of OT, Zero Trust is an even more profound paradigm shift. It means:

1. Eliminating Implicit Trust even for control systems, PLCs, and engineering workstations that have historically been considered “safe” once inside the facility.
2. Continuously Authenticating and Authorizing every human and non-human (machine, application, sensor) entity for every single network session or action.
3. Restricting Access to the bare minimum necessary for an industrial process to function (Least Privilege Access).
4. Implementing Granular Micro-Segmentation to contain any potential breach and prevent lateral movement across the plant floor.

Unlike IT, where performance and confidentiality are key, OT prioritizes Safety and Availability (Availability Integrity Confidentiality – AIC). Any ZTA solution for OT must be engineered to uphold these priorities, respecting the unique constraints of industrial protocols (e.g., Modbus TCP, EtherNet/IP), legacy equipment, and the intolerance for downtime.

The Pillars of OT Zero Trust: Adapting the Framework

While the core principles remain the same, their application in OT requires specialized tools and methodologies.

1. Identity and Access Management (IAM) for OT (The “Who” and “What”)

In OT, identities are not just human operators; they include specialized engineering accounts, machine-to-machine communications, and the assets themselves.

• Multi-Factor Authentication (MFA) and Identity Proofing: Mandatory MFA for all human users (operators, engineers, vendors) accessing Level 3/2 systems (HMIs, Historians, Jump Servers). This must be phishing-resistant where possible.
• Non-Human Identity Management: Treating PLCs, RTUs, and applications as unique identities that require explicit authentication and authorization to communicate.
• Least Privilege/Just-In-Time (JIT) Access: Granting high-privilege access (like programming a PLC) only for a strictly limited duration and scope, automatically revoking it afterward. This is critical for remote vendor access.

2. Device Trust and Posture Assessment (The “How Secure”)

OT environments are rife with legacy devices that cannot run modern security agents. Device Trust in OT focuses on posture monitoring.

• Asset Inventory and Visibility: A comprehensive, real-time inventory of all connected devices (vendor, model, firmware, vulnerabilities) is the absolute prerequisite.
• Behavioral Anomaly Detection: Instead of relying on an agent, the solution monitors the network behavior of the device (e.g., a PLC is suddenly attempting to connect to a different network segment or using a non-standard port).
• Compliance Check: Ensuring devices (especially engineering workstations) are patched, have up-to-date antivirus, and adhere to a security baseline before granting connection.

3. Micro-Segmentation and Policy Enforcement (The “Where” and “When”)

This is the most critical and challenging pillar in OT. Traditional segmentation (Level 3 to Level 2) is no longer enough.

• Policy Enforcement Point (PEP): OT-aware PEPs, often specialized firewalls or gateways, must enforce policies that inspect industrial protocols (like Modbus/DNP3) to ensure only authorized commands and data types pass.
• Flow Mapping: Detailed mapping of every essential communication flow (e.g., HMI to PLC, Historian to SCADA) to build the baseline for the “least-allowed” access policy.
• Containment: If a workstation is compromised, micro-segmentation ensures the threat cannot spread laterally to other control networks or safety-instrumented systems (SIS).

Top Zero Trust Solutions for OT Environments (2025 Edition)

The Zero Trust vendor landscape is diverse, often requiring a combination of IT-centric identity platforms and specialized OT security vendors to achieve a comprehensive architecture. The top solutions for 2025 are those that specifically address the unique constraints of OT with deep-packet inspection, robust protocol support, and non-invasive deployment models.

Here, we break down ten critical solution categories and the major players driving Zero Trust adoption in critical infrastructure:

Category 1: OT-Native Micro-Segmentation and Visibility Platforms

These platforms are the foundation of Zero Trust in the plant, providing the deep context and enforcement required at Purdue Levels 0-3.

1. Dragos Platform

• Zero Trust Focus: Deep operational visibility and threat detection informs precise micro-segmentation policies.
• Core Value: Provides the most comprehensive visibility into OT protocols and communication flows, which is essential for building accurate “least privilege” access policies. Their threat intelligence and behavioral analytics are OT-specific, allowing you to detect and stop lateral movement from compromised IT or engineering systems.

2. Nozomi Networks Guardian

• Zero Trust Focus: Real-time asset inventory, continuous monitoring, and micro-segmentation policy management.
• Core Value: Excels in asset discovery and continuous network monitoring. It provides the traffic flow data needed to define granular policies and integrates with third-party enforcement points (firewalls) to deploy micro-segmentation rules without disrupting the industrial process.

Category 2: Secure Remote Access (SRA) Gateways

Remote access is the number one attack vector into OT. These solutions replace insecure VPNs and RDP jump hosts with a verified, least-privilege gateway.

3. Claroty Platform / Secure Remote Access (SRA)

• Zero Trust Focus: Clientless, zero-trust remote access for third-party vendors and internal staff.
• Core Value: Enforces the “never trust” principle for all remote connections. It provides an authenticated, authorized, and fully recorded session for every user. Importantly, it abstracts the user from the OT network, only allowing a secure, tunneled connection to the specific HMI or engineering tool required, thus limiting the blast radius of a compromised vendor account.

4. XONA Systems

• Zero Trust Focus: Purpose-built ZTNA for critical infrastructure and remote operations.
• Core Value: Offers a secure, clientless gateway that strictly enforces per-session, least-privilege access. Its emphasis on protocol isolation and a thin-client display means the remote user’s device never directly touches the sensitive OT network, significantly reducing the risk of malware propagation.

Category 3: Identity and Privileged Access Management (PAM) Integrators

These tools manage the human and non-human identities, ensuring strict control over who can perform high-risk actions.

5. CyberArk/BeyondTrust (PAM Solutions with OT Context)

• Zero Trust Focus: Securing privileged credentials and enforcing Just-In-Time (JIT) access for high-risk operations.
• Core Value: While historically IT-focused, both vendors now offer solutions that integrate with OT security platforms. They manage the shared or highly-privileged accounts (like local administrators on HMIs or SCADA servers), require check-out/check-in, and provide session recording, ensuring that high-privilege actions are both verified and auditable.

6. Microsoft Entra ID (formerly Azure AD) with Conditional Access

• Zero Trust Focus: Centralized identity plane for IT/OT convergence and access to cloud-connected OT applications.
• Core Value: For industrial organizations leveraging Microsoft cloud services (like Azure IoT or Defender for IoT), Entra ID’s Conditional Access is a powerful Zero Trust policy engine. It can combine signals from an OT device’s security posture (via a solution like Defender for IoT) with a user’s identity and location to make a dynamic access decision for hybrid IT/OT resources.

Category 4: Next-Generation Firewalls (NGFW) with OT Deep Packet Inspection

The firewall remains a Policy Enforcement Point, but in ZTA, it must understand industrial protocols.

7. Palo Alto Networks Next-Generation Firewalls (NGFW)

• Zero Trust Focus: Segmenting the network and inspecting industrial control protocols.
• Core Value: Their NGFWs can apply application-layer enforcement policies that go beyond simple port/protocol filtering. This is crucial for OT, as it allows the firewall to ensure a specific device is only sending valid commands (e.g., a “read coil status” command in Modbus, but not a “write multiple registers” command) to a specific PLC, which is a key tenet of least privilege.

8. Fortinet Security Fabric for OT

• Zero Trust Focus: End-to-end security architecture with integrated ZTNA and OT-aware enforcement.
• Core Value: Fortinet’s strength lies in its integrated Security Fabric, allowing for a cohesive application of Zero Trust principles from the corporate network down to the industrial perimeter. Their FortiGate NGFWs offer OT protocol-aware security and can act as a crucial policy enforcement point for both physical and virtual segmentation within the OT network.

Category 5: Cloud-Based Secure Service Edge (SSE) & Zero Trust Network Access (ZTNA)

As more industrial data moves to the cloud for analytics, ZTNA ensures secure access without ever putting users on the network.

9. Zscaler Zero Trust Exchange for OT/IoT

• Zero Trust Focus: Securing access to industrial cloud applications and providing segmentation for OT/IoT devices.
• Core Value: Zscaler’s cloud-native platform is extending its reach into OT by focusing on isolating devices and providing secure, direct-to-app access. It’s highly effective for manufacturers with hybrid cloud deployments, ensuring that users and devices only connect to the specific application they need, without ever being placed on a flat network.

10. Cisco Zero Trust (Duo and Secure Access)

• Zero Trust Focus: Identity and device verification for both internal and remote access to applications.
• Core Value: Cisco Duo provides foundational, strong MFA and device health checks. When combined with Cisco Secure Access, it forms a cohesive ZTNA solution that can be applied to access SCADA, Historian, and other centralized OT systems from anywhere, based on a continuous risk assessment of the user and the endpoint.

The Unique Challenges of OT Zero Trust Implementation

Deploying a Zero Trust model in an industrial setting is significantly more complex than in a standard IT enterprise. Industrial cybersecurity content writers must be upfront about these hurdles:

1. Legacy Equipment and Protocol Constraints

Many PLCs and control devices are decades old and simply cannot support modern security agents, encryption, or authentication mechanisms (e.g., they may not support TLS/SSL). The ZT solution must be non-invasive, relying on network monitoring, secure proxies, or gateways to enforce policy on their behalf. This often means relying heavily on micro-segmentation and firewall-based policy enforcement rather than endpoint-based trust.

2. The Priority of Availability and Safety

Any security control that introduces latency, requires a reboot, or risks a process shutdown is a non-starter in OT. Policy deployment must be an “observe, model, and safely enforce” process. The initial phase of ZTA in OT is almost entirely about non-invasive asset discovery and traffic flow analysis to model the “least-allowed” baseline before any enforcement is applied.

3. Change Management and Organizational Silos

The people who own the IT network are often different from the people who own the OT network (Control Engineers vs. IT Security). A successful ZTA project requires a unified governance model and cross-functional teams to agree on a single, integrated security policy that serves both security requirements and operational needs.

4. Continuous Monitoring in the OT Context

Zero Trust demands continuous monitoring and re-authentication. In OT, this means continuously monitoring the behavior of devices and industrial processes. An unauthorized change to a PLC’s logic, or an unusual Modbus command, must trigger an immediate and automated response from the Policy Engine to revoke the trust and block the session-a level of process awareness that generic IT solutions lack.

A Roadmap for Your OT Zero Trust Journey

Zero Trust in OT is not a single product purchase; it is a strategic, multi-year journey. Here is a practical, phased approach:

Phase 1: Establish Foundational Visibility (3-6 Months)

• Action: Deploy non-invasive, passive asset discovery and network monitoring tools (e.g., Dragos, Nozomi, Claroty) to get 100% visibility into all assets, vulnerabilities, and traffic flows in the OT network.
• ZT Principle: Define the “Protect Surface” (critical assets).
• Key Deliverable: A complete, high-fidelity OT asset inventory and a validated map of all critical transaction flows.

Phase 2: Secure the Human and Remote Access (6-12 Months)

• Action: Implement a Secure Remote Access (SRA) gateway (e.g., XONA, Claroty SRA) for all third-party and remote internal access. Mandate phishing-resistant MFA for all human users accessing critical OT systems.
• ZT Principle: Explicitly Verify Identity and Enforce Least Privilege Access for humans.
• Key Deliverable: Elimination of all insecure VPN and RDP-based remote access.

Phase 3: Implement Strategic Segmentation (12-24 Months)

• Action: Begin with macro-segmentation (IT/OT demilitarized zone – IDMZ) using an OT-aware NGFW. Then, implement granular micro-segmentation policies based on the flow maps created in Phase 1, focusing first on critical zones like the Safety Instrumented System (SIS) network.
• ZT Principle: Limit the “Blast Radius” through Micro-segmentation.
• Key Deliverable: Policy-driven communication between control system components that only allows essential, validated industrial protocols and commands.

Phase 4: Continuous Verification and Automation (Ongoing)

• Action: Integrate identity, SRA, and network monitoring platforms so that behavioral anomalies (e.g., a high-risk security score from a behavioral platform) can automatically feed into the Policy Engine to dynamically revoke or degrade access for a user or device.
• ZT Principle: Assume Breach and enforce Continuous Verification.
• Key Deliverable: A dynamic, adaptive security model where access is granted not just on identity, but on continuous context, device health, and real-time operational risk.

Conclusion: The Resilient Industrial Future

The Zero Trust architecture is not a passing trend; it is the inevitable future of industrial cybersecurity. The era of trusting what is inside the fence is over. By strategically selecting OT-native solutions and adapting ZT principles to respect the inviolable requirements of industrial safety and availability, critical infrastructure organizations can move beyond mere perimeter defense to achieve true cyber-physical resilience.

The next industrial revolution demands a security model that can keep pace with connectivity, and the solutions outlined above are leading the charge in making the “never trust, always verify” standard a reality on the plant floor.