CIS Benchmark for Operational Technology (OT) Environments

What Makes CIS Benchmarks for OT Different from IT

The core distinction between IT-focused CIS Benchmarks and those designed for OT environments lies in the risk calculus. In IT, the primary concern is data confidentiality, integrity, and availability—in that order. In OT, availability and safety are paramount. A misconfigured firewall rule that causes a PLC to lose communication for two seconds might halt an assembly line, trigger a safety shutdown, or, in worst cases, cause physical damage. Standard CIS Benchmarks for Windows Server or Linux, if applied blindly to OT assets, would almost certainly break critical industrial processes.

OT-specific CIS Benchmarks address this by:

• Filtering recommendations by impact — Each configuration setting is evaluated for its potential to disrupt operational processes.
• Accounting for legacy systems — Many OT environments run Windows Embedded, legacy Windows NT/2000, or proprietary real-time operating systems that do not support modern security controls.
• Addressing industrial protocols — Benchmarks cover protocols such as Modbus, DNP3, OPC, and Profinet, which have no equivalent in standard IT.
• Segmenting by ICS component type — Separate guidance exists for Human-Machine Interfaces (HMIs), engineering workstations, historians, controllers, and network infrastructure.

The Core Structure of CIS Benchmarks for OT

The CIS Benchmark for OT environments follows the same general framework as other CIS Benchmarks but with significant modifications to the recommendation levels and applicability scope. Each benchmark is organized into sections corresponding to functional areas of an OT deployment.

Configuration Recommendation Levels

CIS Benchmarks for OT use a modified classification system that reflects the operational criticality of each setting:

Key Benchmark Categories

A typical CIS Benchmark for OT covers the following domains, each with its own set of specific hardening recommendations:

• Account and access control — Restricting interactive logins to HMIs and engineering workstations, disabling unused local accounts, enforcing privileged access management for control system access.
• Authentication and password policies — Configuring password complexity and lockout policies that do not interfere with emergency access or safety override procedures.
• Logging and auditing — Enabling security event logging on historian servers and domain controllers serving OT zones, while avoiding excessive logging on resource-constrained controllers.
• Network segmentation and firewall rules — Configuring industrial firewalls and unidirectional gateways, restricting traffic between IT and OT zones, and limiting protocols to only those required.
• Patch and update management — Establishing tested patch cycles for OT assets, maintaining air-gapped update repositories, and documenting known exceptions for unsupported systems.
• Physical and environmental security — Locking down console access to controllers, disabling USB ports on HMIs, and securing network jacks in control rooms.
• Secure configuration of industrial protocols — Disabling unused protocol services, enforcing authentication where available (e.g., DNP3 Secure Authentication), and monitoring for anomalous protocol traffic.

Why Standard IT CIS Benchmarks Fail in OT

The most common mistake organizations make when beginning OT hardening is applying standard IT CIS Benchmarks to industrial assets. The consequences range from annoying to catastrophic.

Operational Disruption Risks

Standard CIS Benchmarks for Windows Server, for example, recommend disabling legacy protocols like SMBv1, enabling Windows Defender, and enforcing strict account lockout policies. In an OT context:

• Many legacy HMIs and SCADA systems rely on SMBv1 for file sharing between engineering workstations and historians. Disabling it can break critical data flows.
• Real-time antivirus scanning on a PLC or RTU can introduce latency that disrupts control loops.
• Aggressive account lockout policies can lock out operators during shift changes or emergency response, creating safety hazards.

The Gap in Protocol and Device Coverage

Standard IT benchmarks have no guidance for industrial protocols such as Modbus TCP, DNP3, Profinet, EtherNet/IP, or OPC UA. They also do not cover the configuration of industrial switches, remote terminal units (RTUs), PLCs, or distributed control system (DCS) controllers. Attempting to assess OT assets using a tool like CIS-CAT with standard IT benchmarks will result in a high number of "not applicable" or "failed" findings that have no operational meaning, creating noise that obscures real security issues.

How to Implement CIS Benchmarks in OT Environments

Implementing CIS Benchmarks in OT requires a phased, risk-aware approach that respects the operational reality of industrial systems. The following process is recommended for organizations at any stage of OT security maturity.

CIS Benchmarks and the Purdue Model

The Purdue Enterprise Reference Architecture (often called the Purdue Model) provides a useful framework for understanding where CIS Benchmarks apply in an OT environment. Different levels of the model require different benchmark profiles and enforcement approaches.

This layered approach ensures that security controls are applied proportionally—strongest at the upper levels where IT-like systems operate, and most conservative at the lower levels where real-time control and safety are paramount. The top 10 CIS benchmarking tools evaluation from CyberSilo provides detailed comparisons of solutions that support this multi-level OT benchmarking approach.

CIS Benchmarks vs. DISA STIG for OT

Organizations operating OT environments under U.S. Department of Defense (DoD) contracts or within the defense industrial base (DIB) often need to choose between CIS Benchmarks and DISA STIGs (Security Technical Implementation Guides). Both frameworks offer OT-specific guidance, but they differ in key ways.

For most commercial OT environments, CIS Benchmarks offer the better balance of security value and operational safety. For defense-related OT, organizations may need to comply with both—using CIS Benchmarks as the baseline and overlaying applicable STIGs where required by contract or regulation.

Automating CIS Benchmark Assessment in OT

Manual assessment of OT asset configurations is impractical for any environment larger than a handful of devices. The operational cost, risk of human error, and inability to track configuration drift over time make automation essential. However, OT environments present unique challenges for automated assessment tools.

Challenges of Automated Scanning in OT

• Network fragility — Active scanning of legacy controllers can cause them to crash or lose communication. Many PLCs and RTUs were never designed to handle the traffic patterns generated by vulnerability scanners or configuration assessment tools.
• Proprietary interfaces — Industrial equipment often uses proprietary management interfaces that standard assessment tools cannot read. Vendor-specific tools or APIs may be required.
• Air-gapped or segmented networks — Critical OT zones are often air-gapped or separated by unidirectional gateways, making it difficult to deploy centralized assessment agents.
• Resource constraints — Many OT devices have limited memory and processing power, making it impossible to run agents or even respond to complex scan queries.

Safe Automation Approaches

Despite these challenges, automated CIS Benchmark assessment is achievable in OT environments using the following approaches:

• Passive assessment — Monitoring network traffic via SPAN ports or network taps to infer configuration state without actively querying devices. This is the safest approach for Level 0–2 assets.
• Agent-based on supported platforms — Deploying lightweight assessment agents on Windows-based HMIs, engineering workstations, and historian servers where operational impact is acceptable.
• Configuration file analysis — Exporting configuration files from controllers and analyzing them offline against CIS Benchmark criteria. Many modern PLCs and RTUs support configuration export for backup and audit purposes.
• Orchestrated assessment via OT-specific platforms — Using purpose-built OT security platforms that integrate with common industrial control system vendors (Rockwell, Siemens, Schneider Electric, ABB, etc.) to query configuration state through vendor-approved interfaces.

Integrating CIS Benchmarks with OT Compliance Frameworks

CIS Benchmarks for OT do not exist in isolation. They are increasingly referenced by regulatory frameworks and industry standards as a means of demonstrating compliance with broader security requirements.

NERC CIP

The North American Electric Reliability Corporation Critical Infrastructure Protection (NERC CIP) standards require entities to implement configuration management and change control for cyber assets within the bulk electric system. While NERC CIP does not mandate a specific benchmark, CIS Benchmarks for OT are widely accepted as a reasonable and defensible approach to meeting CIP-005 (Electronic Security Perimeter), CIP-007 (Systems Security Management), and CIP-010 (Configuration Change Management) requirements. Many utilities use CIS Benchmarks as their "baseline security configuration" referenced in CIP-010.

IEC 62443 / ISA-62443

The IEC 62443 series of standards for industrial communication networks and system security is the de facto international standard for OT cybersecurity. CIS Benchmarks for OT map directly to several IEC 62443 requirements, particularly those in:

• IEC 62443-2-1 — Security program requirements for system operators
• IEC 62443-3-3 — System security requirements and security levels
• IEC 62443-4-2 — Technical security requirements for IACS components

Applying CIS Benchmarks helps organizations achieve specific security levels (SLs) defined by IEC 62443, particularly for hardening of control system components and network infrastructure.

NIST SP 800-82

NIST Special Publication 800-82, Guide to Industrial Control Systems Security, includes configuration hardening as a key security control across multiple domains. CIS Benchmarks for OT provide the specific, actionable configuration guidance that NIST 800-82 recommends but does not prescribe in detail. Organizations using NIST 800-82 as their OT security framework can use CIS Benchmarks as the implementation mechanism for controls in the Access Control, Configuration Management, and System and Information Integrity families.

EU NIS2 Directive

The NIS2 Directive, which entered into force across European Union member states in 2024, identifies essential and important entities in sectors including energy, transport, manufacturing, water supply, and chemical production. NIS2 requires these entities to implement "appropriate and proportionate technical and operational measures" to manage security risks. While NIS2 does not mandate specific benchmarks, demonstrating compliance with CIS Benchmarks for OT is increasingly viewed by national regulators as evidence of due diligence in configuration hardening.

Common Pitfalls in OT CIS Benchmark Implementation

Even organizations that adopt OT-specific CIS Benchmarks often encounter challenges that undermine their effectiveness. The following pitfalls are particularly common in enterprise OT environments.

Treating OT Like IT

The most persistent pitfall is applying IT-centric security thinking to OT environments. This manifests in several ways: scheduling scans during business hours without understanding shift patterns in continuous process environments, expecting software-based patching for embedded devices that have no update mechanism, or requiring quarterly password changes on HMIs that operators use in emergency situations where rapid access is safety-critical. OT security requires a fundamentally different operational tempo and risk acceptance threshold.

Ignoring the Human Element

OT environments often have long-tenured operators and engineers who are deeply knowledgeable about the industrial processes but may resist security changes that they perceive as interfering with production. Without their buy-in, configuration hardening initiatives will fail. Successful implementations include operators and control engineers in the benchmarking process, clearly communicating the safety and reliability benefits of security hardening, and involving them in the testing and validation of configuration changes.

Failing to Monitor for Drift

Many organizations perform a one-time CIS Benchmark assessment, achieve a target hardening score, and then never reassess. In OT environments, configuration drift is constant—operators disable security features to troubleshoot problems, vendors install updates that change settings, and engineer workstations are rebuilt without remembering to reapply security configurations. Continuous or periodic re-assessment is essential. This is where the top 10 compliance automation tools evaluated by CyberSilo can help maintain ongoing visibility into configuration state across IT and OT domains.

Over-Securing Non-Critical Assets While Neglecting Critical Ones

It is common to find organizations that have hardened their IT side of the OT network (Level 4–5) extensively while leaving Level 1–2 controllers completely unassessed. This creates a false sense of security—the perimeter may be strong, but the crown jewels are soft. The Purdue Model-based approach described earlier ensures that assessment effort is proportional to risk, with the most critical assets receiving the most focused attention, even if the number of applicable controls is smaller.

The Business Case for OT CIS Benchmarking

For CISOs and security leaders responsible for OT environments, the business case for implementing CIS Benchmarks rests on four pillars:

• Risk reduction — Configuration hardening is consistently cited in incident reports as one of the most effective defenses against ransomware and targeted attacks on industrial systems. The 2021 Colonial Pipeline incident was enabled in part by poor configuration management and credential hygiene.
• Compliance demonstration — Regulators across multiple sectors (energy, water, chemical, transportation) are increasingly expecting documented configuration hardening programs. CIS Benchmarks provide a defensible, third-party-validated standard.
• Insurance and liability — Cyber insurance underwriters for OT environments are beginning to ask about configuration management practices. Having a documented CIS Benchmark assessment program can positively influence coverage terms and premiums.
• Operational resilience — Hardened configurations, when properly validated, reduce the attack surface without compromising operational availability. In fact, many CIS Benchmark recommendations (such as disabling unused services and restricting unnecessary network connections) improve system stability by reducing the potential for unintended interactions.

Future Direction of CIS Benchmarks for OT

The CIS community continues to expand its OT coverage as industrial environments evolve. Key trends shaping the future of OT CIS Benchmarks include:

• Cloud-connected OT — As more OT systems connect to cloud-based monitoring and analytics platforms, benchmarks are being developed for hybrid architectures that bridge on-premises controllers with cloud services.
• 5G for industrial networks — Private 5G networks in manufacturing and energy facilities require new benchmarks for base station configuration, network slicing security, and device authentication.
• IoT edge devices — The proliferation of industrial IoT sensors and actuators introduces new device types that fall outside traditional OT benchmarks. CIS is developing guidance for these constrained devices.
• AI/ML in control systems — As machine learning models are deployed for predictive maintenance and process optimization, benchmarks will need to address the security of the model lifecycle, training data integrity, and runtime monitoring.
• Software-defined OT — The move toward software-defined control systems and virtualized PLCs requires benchmarks for hypervisor configuration, container security, and software-defined networking in industrial contexts.