The short version.
To assess OT risk, define the scope, identify threats and vulnerabilities, rate each risk by impact and likelihood, then plan, document and track the fixes.
Start by listing the systems in scope, such as PLCs, SCADA systems and network devices. Rate each threat and vulnerability pair on a risk matrix of low, medium and high. Impact covers downtime, data loss and safety hazards.
Record each risk and its mitigation in a risk register. Re-run the assessment after any significant change, such as new equipment or a network redesign.
Introduction
CMMC and NIST 800-171 require a risk assessment of your OT environment. This guide covers the steps, tools and practices for an OT risk assessment.
Why OT risk assessments matter
What a risk assessment does
A risk assessment finds the weaknesses and threats that could stop your operations. OT environments often include legacy systems and critical infrastructure that cannot tolerate downtime, which IT systems rarely do. A risk assessment helps you with:
- Identifying Vulnerabilities: You find the weaknesses an attacker could exploit.
- Prioritizing Risks: You work first on the risks with the largest impact on operations.
- Complying with Regulations: You meet the requirements of frameworks like CMMC and NIST 800-171.
- Choosing controls: You pick the controls that reduce each risk.
Compliance and Regulatory Standards
NIST SP 800-171 and CMMC set the rules for managing cybersecurity risk where controlled unclassified information is stored or processed. For industrial control systems more broadly, NIST SP 800-82 and IEC 62443 give guidance on assessing and reducing OT risk.
Steps to Perform a Risk Assessment
1. Define the Scope
First, decide which systems, processes and data the assessment covers:
- Systems: Identify all OT systems that are critical to operations, including PLCs, SCADA systems, and network devices.
- Processes: Document the processes that rely on these systems.
- Data: Determine the sensitive data processed or stored within these systems.
2. Identify Threats and Vulnerabilities
Next, list the threats and vulnerabilities that apply to the systems in scope:
- Threat Modeling: Identify potential threat actors, their capabilities, and intent.
- Vulnerability Assessments: Use tools and techniques to identify vulnerabilities in your systems. These can include outdated software, misconfigurations, or weak access controls.
3. Assess the Impact and Likelihood
For each threat, estimate what happens if it exploits a vulnerability and how likely that is:
- Impact Analysis: Determine the potential consequences of a threat exploiting a vulnerability, such as downtime, data loss, or safety hazards.
- Likelihood Estimation: Assess how likely it is for each threat to occur, considering factors like threat actor capability and existing controls.
4. Determine Risk Levels
Combine impact and likelihood to get a risk level for each threat and vulnerability pair. A risk matrix shows each risk as low, medium or high.
5. Develop Mitigation Strategies
For each risk, choose controls that reduce its impact or likelihood:
- Technical Controls: Implement firewalls, intrusion detection systems, and access controls.
- Administrative Controls: Develop policies and procedures for security management.
- Physical Controls: Secure physical access to critical systems.
6. Document and Report Findings
Write up the findings and share them with the people who own the risks. The report should include:
- Risk Register: A detailed list of identified risks, their levels, and mitigation strategies.
- Recommendations: The steps that will reduce each risk.
- Compliance Alignment: How the risk assessment aligns with relevant compliance standards.
Best Practices for OT Risk Assessments
Involve IT, operations and compliance
Involve IT, operations and compliance staff. Each group knows risks the others miss.
Use Automated Tools
Use automated tools for vulnerability scans. Intrusion detection systems and network traffic analyzers show unusual activity.
Monitor and Update the Assessment
Run the assessment more than once. Monitor your OT environment for new threats and vulnerabilities, and update the assessment when your environment or the threats against it change.
Align with Compliance Frameworks
Map your risk assessment process to the frameworks you must meet, such as CMMC, NIST 800-171 and IEC 62443.
What to do next
An OT risk assessment produces a prioritized list of vulnerabilities, their potential impact on physical processes, and the controls needed to mitigate them. Run the assessment annually at minimum, and re-run it after any significant change to your OT environment (new equipment, network redesign, new site connection). Map each identified risk to the specific CMMC, NIST 800-171, or IEC 62443 control that addresses it, and track remediation to completion.