Operational Technology
Risk-Based Patch Calculation

A strategic process for deciding when and how to apply security patches to industrial control systems, SCADA, PLCs, and plant-floor devices based on measured risk rather than immediate deployment.

Why Risk-Based Patching Matters

OT environments have unique constraints including 24×7 production requirements, safety considerations, and extensive testing needs. A risk-based approach helps prioritize limited maintenance windows while reducing cyber risk effectively.

Safety First

Avoids unplanned downtime or accidents from rushed updates

Compliance Support

Supports standards like IEC 62443, NIST SP 800-82, and ISO 27019

Resource Optimization

Focuses effort where it reduces the most risk

Key Elements of Risk-Based Calculation

Six critical components that form the foundation of effective OT security patch management

Asset Criticality

Identify how important each system is to safety, production, or compliance.

Example metrics: safety impact, regulatory impact, production loss cost

Vulnerability Severity

Use vulnerability scoring (e.g., CVSS) and vendor advisories to gauge exploitability.

Example metrics: CVSS scores, vendor advisories, exploitability metrics

Threat Likelihood

Consider active exploitation, exploits in the wild, and asset exposure.

Example metrics: network accessibility, exploit availability, threat intelligence

Compensating Controls

Evaluate if firewalls, segmentation, or access controls reduce immediate patch needs.

Example metrics: network segmentation, access controls, monitoring systems

Operational Constraints

Determine maintenance windows, redundancy, and testing requirements.

Example metrics: maintenance windows, system redundancy, safety requirements

Risk Scoring Formula

Compute risk scores to prioritize patching decisions effectively.

Example metrics: mathematical models, priority matrices, decision frameworks

Risk Scoring Formula

A mathematical approach to quantify and prioritize security risks

Risk Score = (Asset Criticality × Vulnerability Severity × Threat Likelihood) ÷ Compensating Controls

This formula provides a quantitative foundation for patch prioritization decisions, though the exact implementation may vary based on organizational standards and compliance requirements.

Patch Priority Framework

High Risk

Urgent patch or immediate mitigation required

Timeframe: Emergency maintenance window

Medium Risk

Schedule during next planned maintenance

Timeframe: Next scheduled outage

Low Risk

Monitor and rely on existing controls

Timeframe: Future maintenance cycles

Risk-Based Patch Priority

This model helps you prioritize vulnerabilities by combining CVSS with environmental context to produce a composite risk score.