Best practices for OT Security architecture review

An OT security architecture review is more than just a checklist item to be considered once a while; instead, it is a strategic assessment designed to identify weaknesses, mitigate risks, and ensure your industrial control systems (ICS) are protected against evolving cyberattacks. An OT security architecture review can provide unmatched clarity and data points for security decision making.

Let's dive into some best practices for conducting these crucial reviews.

Don’t forget to read our previous blog on How to choose the best OT Security Platform for your industrial operations.

Start with a strong foundation: IEC 62443 and NIST

Don't reinvent the wheel. Leverage established industry standards as the backbone of your review process.

· IEC 62443 (Industrial Automation and Control Systems Security): This is the gold standard and a North Star for OT security best practices. It provides a structured approach to cybersecurity for industrial control systems, covering everything from system design and development to operations and maintenance.

· So how can you apply IEC 62443 to an OT security architecture review: During a review, map your architecture against the different parts of IEC 62443 (e.g., 62443-2-1 for security program requirements, 62443-3-3 for system security requirements). This helps ensure you're addressing security at every layer and throughout the lifecycle. Pay close attention to defining security zones and conduits, a fundamental concept in IEC 62443 for segmenting your OT network based on trust levels. You can use IEC 62443 to ensure the establishment of a robust architecture that secures your assets and networks.

· NIST Cybersecurity Framework (CSF) and NIST SP 800-82 (Guide to Industrial Control System Security): While the NIST CSF provides a high-level framework for managing cybersecurity risk across an enterprise, NIST SP 800-82 specifically tailors these principles to ICS.

· How to apply it: Use the NIST CSF's five functions (Identify, Protect, Detect, Respond, Recover) to structure your review. SP 800-82 offers detailed guidance on implementing security controls relevant to OT environments, including considerations for legacy systems and the unique operational constraints of ICS.

By aligning with these standards, you ensure your review is comprehensive, globally recognized, and focused on genuine OT risks. Such alignments can also be helpful for ensuring compliance with regulatory mandates and to prove the adherence to best OT security practices.

Embrace simplification: The power of clarity

Overly intricate architectures are harder to understand, manage, and secure, leading to hidden vulnerabilities and increased operational overhead. At a fundamental level, they can bring forth blind spots that can hamper everything from asset visibility to delayed Incident Response.

· Zone and conduit simplification: While IEC 62443 emphasizes zones and conduits, it's easy to over-engineer these. Strive for the fewest necessary zones, clearly defined by their function and trust level. Each conduit (the communication path between zones) should have tightly controlled access rules. A simplified zone model makes it easier to enforce segmentation and monitor traffic.

· Minimalist design: Can a control system perform its function with fewer network connections, fewer services running, or fewer open ports? Often, the answer is yes. Adopt a "least functionality" approach, enabling only what is absolutely necessary for operations.

· Documentation Clarity: Simple architectures are easier to document accurately. Clear, up-to-date network diagrams, asset inventories, and data flow maps are invaluable for both security and operational teams.

Deep dive: Major areas of focus

A thorough review goes beyond surface-level checks. Here are critical areas to scrutinize:

· Network Segmentation: Is your OT network truly isolated from your IT network? Within OT, are critical process control systems segmented from less critical components? Micro-segmentation strategies should be evaluated for effectiveness.

· Visibility: Into assets, networks, policy enforcement and tracking measures to ensure security practices are monitored

· Remote Access: How are third parties and internal personnel accessing OT systems remotely? Is multi-factor authentication (MFA) enforced? Are sessions monitored and logged?

· Vulnerability Management: What's your process for identifying and patching vulnerabilities in OT assets? Acknowledge that patching may not always be feasible in OT, requiring compensatory controls. In such situations, do you have the ability to deploy appropriate compensatory controls?

· Identity and Access Management (IAM): Are user accounts managed centrally? Are strong passwords enforced? Is the principle of least privilege applied rigorously to both human and machine accounts?

· Data Flow Analysis: Understand exactly what data flows between which systems, and why. This helps identify unauthorized communication paths or potential exfiltration points.

· Backup and Recovery: In the event of an incident, can critical systems be safely and quickly restored? Test your recovery plans regularly.

· Physical Security: Don't forget the basics. Physical access to control rooms, servers, and network equipment is a foundational element of OT security.

Engage diverse stakeholders

An effective OT security architecture review requires input from various teams:

· OT Engineers/Operators: They understand the operational imperatives, potential impact of security measures, and the unique characteristics of the industrial processes.

· IT Security Professionals: They bring cybersecurity best practices and threat intelligence from the IT domain.

· Management: To ensure alignment with business objectives and allocate necessary resources.

· OEMs and third-party vendors

· External Experts: Consider bringing in specialized OT cybersecurity consultants for an objective perspective and deep expertise, especially with complex architectures or compliance requirements.

Document everything and follow up

A review is only valuable if its findings lead to action.

· Detailed Report: Document all findings, identified risks, recommended remediation steps, and assign ownership for each action item. Prioritize findings based on risk level.

· Roadmap for Improvement: Develop a clear roadmap for implementing changes. Some improvements may be quick wins, while others require long-term planning and investment.

· Regular Cadence: OT environments are dynamic. Schedule regular architecture reviews (annually, or more frequently for significant changes) to adapt to new threats, technologies, and operational requirements.

A robust OT security architecture is your first line of defense against potentially catastrophic cyber incidents. By adopting best practices grounded in standards like IEC 62443 and NIST, embracing architectural simplification, focusing on critical areas, and engaging all relevant stakeholders, organizations can build and maintain a resilient OT security posture that protects their vital industrial operations. Your efforts today will safeguard the infrastructure of tomorrow.

Learn more about Shieldworkz OT Security Architecture Review offering.