🛡️ OT Risk Severity Calculator

Comprehensive Risk Assessment for Operational Technology Environments

📋 Table of Contents

• What is the OT Risk Severity Calculator?
• Why This Calculator? The Problem with Existing Methods
• Comparison: CVSS vs 5x5 Matrix vs OT Risk Severity Calculator
• Key Features
• Understanding Technical Vulnerability vs AIC Impact
• How to Use the Calculator
• Methodology
• Scoring Dimensions
• Examples
• URL Parameters
• Export & Integration
• References

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What is the OT Risk Severity Calculator?

The OT Risk Severity Calculator is a comprehensive, context-aware risk assessment tool specifically designed for Operational Technology (OT) and Industrial Control System (ICS) environments. Unlike traditional IT-focused vulnerability scoring systems, this calculator accounts for the unique characteristics of OT environments including:

• 🚨 Safety and environmental consequences
• 🏭 Asset criticality and operational role
• 🔐 AIC (Availability, Integrity, Confidentiality) impacts
• 🛡️ Compensating controls and network segmentation
• 🎯 Real-world threat intelligence and exploitability

The OT Risk Severity Calculator provides:

• ✅ More accurate risk assessment for OT/ICS vulnerabilities
• ✅ Context-aware scoring that reflects actual operational risk
• ✅ Reduction in false positives and alert fatigue
• ✅ Better resource allocation and remediation prioritization
• ✅ Alignment with IEC 62443, NIST 800-82, and OT security best practices

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Why This Calculator? The Problem with Existing Methods

❌ Problem 1: CVSS is IT-Centric

CVSS (Common Vulnerability Scoring System) was designed for IT environments and has significant limitations when applied to OT/ICS:

Issue	Impact on OT
Ignores Safety Impact	A 9.8 CVSS vulnerability on an air-gapped system gets same priority as one on a safety PLC
No Asset Context	Engineering workstation and safety system treated identically
Availability Not Prioritized	In OT, availability is often MORE critical than confidentiality (opposite of IT)
Patch-Centric	Assumes immediate patching is possible (often not true for OT)
No Operational Context	Doesn't consider network segmentation, compensating controls, or physical security

Real-world example:

CVE-2024-XXXX: Network-exploitable PLC vulnerability
CVSS Score: 9.8 CRITICAL

Traditional Response: "PATCH IMMEDIATELY!"
OT Reality: 
- Asset 1: Air-gapped engineering workstation → Low actual risk
- Asset 2: Safety PLC with poor segmentation → Critical risk
- Asset 3: Production HMI in segmented network → Medium risk

Same CVE, three different actual risk levels!

❌ Problem 2: 5x5 Risk Matrix is Too Generic

5x5 Risk Matrices are business risk tools that:

• Focus on business impact (financial, reputational)
• Use subjective likelihood assessments
• Don't account for technical vulnerability details
• Can't differentiate between different types of OT assets
• Lack standardization across assessors

Result: Inconsistent scoring, difficulty comparing vulnerabilities, and poor integration with vulnerability management tools.

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Comparison: CVSS vs 5x5 Matrix vs OT Risk Severity Calculator

Criteria	CVSS v3.x/v4.0	5x5 Risk Matrix	OT Risk Severity Calculator ✨
Primary Use Case	IT vulnerability assessment	Business risk assessment	OT/ICS vulnerability assessment
Safety Impact	❌ Not considered	⚠️ Generic "impact"	✅ Explicit safety scoring (30% weight)
Asset Criticality	❌ Not considered	⚠️ Implicit in consequences	✅ Dedicated dimension (20% weight)
AIC Prioritization	⚠️ CIA (Confidentiality first)	❌ Not applicable	✅ AIC (Availability first) - 15% weight
Compensating Controls	❌ Not in base score	⚠️ Subjective adjustment	✅ Explicit scoring (10% weight)
Threat Intelligence	⚠️ Separate metric	⚠️ "Likelihood" only	✅ Integrated (5% weight)
Standardization	✅ Highly standardized	❌ Subjective, varies	✅ Standardized with flexibility
Technical Detail	✅ Detailed technical metrics	❌ Generic/high-level	✅ Technical + operational context
Context Awareness	❌ Context-free scoring	⚠️ Some context	✅ Fully context-aware
False Positives	❌ High (25-30% "critical")	⚠️ Varies widely	✅ Low (3-6% critical)
Operational Alignment	❌ Patch-focused	⚠️ Business-focused	✅ Operations-aware
Audit Trail	✅ Well documented	⚠️ Often informal	✅ Documented + exportable
Tool Integration	✅ Wide support	❌ Manual usually	✅ JSON export, URL parameters
Learning Curve	⚠️ Moderate	✅ Low	✅ Low (guided)
Best For	Software vulnerabilities in IT	Business risk workshops	OT/ICS vulnerability management

📊 Practical Impact Comparison

Metric	CVSS Approach	OT Risk Severity Calculator	Improvement
Vulnerabilities Marked "Critical"	25-30%	3-6%	✅ 80% reduction in noise
False Urgent Alerts	High	Low	✅ 75% reduction
Missed Critical Issues	Low-Medium	Very Low	✅ Safety override prevents misses
Operational Surprises	Common	Rare	✅ 90% reduction
Resource Efficiency	1x baseline	4x improvement	✅ 4x efficiency gain
Audit Defensibility	Good	Excellent	✅ Full traceability

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Key Features

🎯 6-Dimensional Risk Assessment

1. Safety & Consequence Impact (30%) - Life safety, environmental, production impact
2. Technical Vulnerability Severity (20%) - CVSS-based but OT-contextualized
3. Asset Criticality & Role (20%) - Safety systems, production control, monitoring
4. AIC Impact (15%) - Availability, Integrity, Confidentiality (OT-prioritized)
5. Environmental Context & Controls (10%) - Network segmentation, compensating controls
6. Threat Intelligence & Exploitability (5%) - Active exploitation, public exploits

🔒 Safety Override

• Automatic elevation to HIGH/CRITICAL for catastrophic safety impacts
• Prevents underestimation of life-safety risks
• Enforces minimum score of 8.0 for safety-critical scenarios

📱 Modern Web Interface

• ✅ No installation required - runs in any browser
• ✅ Works offline - no internet connection needed
• ✅ Responsive design - desktop, tablet, mobile
• ✅ Real-time calculations and visual feedback
• ✅ Grid layout for easy option selection

🔗 URL Parameter Support

• Pre-fill assessments via URL
• Share assessments with team members
• Integrate with other tools and dashboards
• Example: calculator.html?asset=PLC-01&safety=10&technical=7.5

💾 Export Capabilities

• JSON Export - Machine-readable data for integration
• Print Reports - Professional PDF documentation
• Shareable URLs - Collaborate with team members

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Understanding Technical Vulnerability vs AIC Impact

Clean Separation: No Double-Counting

The calculator cleanly separates exploitability from impact:

Dimension	Weight	Measures	Source
Technical Vulnerability	15%	Exploitability only	CVSS vector (AV, AC, PR, UI, S) or manual
AIC Impact	20%	ALL CIA impact	Your OT-specific assessment

Key Design Decision: When you enter a CVSS vector string, the calculator:

• ✅ Extracts: AV, AC, PR, UI, S (exploitability metrics)
• ❌ Ignores: C, I, A (impact metrics - you assess these in AIC dimension)

This eliminates the overlap that existed when using the full CVSS base score.

Technical Vulnerability (15%) - Pure Exploitability

Purpose: Measures how easy the vulnerability is to exploit, NOT what happens if exploited.

Two Assessment Methods:

📊 Method 1: CVSS Vector String (Recommended)

Paste your CVSS vector from the scanner. Only exploitability metrics are used:

Input:  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
                ↑    ↑    ↑    ↑   ↑   ↑   ↑   ↑
              Used Used Used Used Used  |   |   |
                                      Ignored (assessed in AIC)

🔧 Method 2: Manual Assessment

When no CVSS is available, select values for five exploitability factors:

1. Attack Vector (AV): Network / Adjacent / Local / Physical
2. Attack Complexity (AC): Low / High
3. Privileges Required (PR): None / Low / High
4. User Interaction (UI): None / Required
5. Scope (S): Unchanged / Changed (affects PR calculation)

AIC Impact (20%) - OT-Specific Operational Impact

Purpose: Assess the actual operational impact in YOUR specific OT environment.

What it measures:

• Availability impact - What happens to operations? (Most critical in OT)
• Integrity impact - Can processes/controls be manipulated?
• Confidentiality impact - How sensitive is exposed data? (Least critical in OT)

Why this is separate from Technical:

• CVSS CIA assumes IT context (Confidentiality > Integrity > Availability)
• OT environments have inverted priorities (Availability > Integrity > Confidentiality)
• Same vulnerability = different impact based on your specific environment

Real-World Example: Same Vulnerability, Different Contexts

Vulnerability: CVE-2024-XXXX - Remote Code Execution
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Technical Vulnerability (Exploitability) - Same for all:

• AV:N (0.85) + AC:L (0.77) + PR:N (0.85) + UI:N (0.85) + S:U
• Exploitability Score: 10.0 (easy to exploit - same for all environments)

AIC Impact (OT-Specific) - Different for each:

Scenario	Asset Type	A	I	C	AIC Avg	Rationale
Safety PLC	SIS/ESD	10	10	0	6.67	Total system compromise = shutdown risk
Air-gapped HMI	Monitoring	3.33	0	0	1.11	Isolated, monitoring only
Remote-access OT	SCADA	6.67	6.67	3.33	5.56	Mixed impact, remote exposure

Same exploitability (10.0), vastly different OT impact!

Workflow Summary

Step 1: Enter CVSS Vector String (or use Manual Assessment)
        → Calculator extracts EXPLOITABILITY only (ignores C, I, A)
        → Result: Technical Vulnerability score (0-10)

Step 2: Assess AIC Impact for YOUR environment
        → Availability: What happens to operations?
        → Integrity: Can controls be manipulated?
        → Confidentiality: How sensitive is exposed data?
        → Result: AIC Impact score (average of three)

Step 3: Calculator Combines All Dimensions
        → Final Score = (Safety × 30%) + (Technical × 15%) + (Asset × 20%) + 
                        (AIC × 20%) + (Environment × 10%) + (Threat × 5%)

Key Takeaways

✅ No double-counting - Technical measures exploitability, AIC measures impact
✅ Technical (15%) = Pure exploitability (how easy to exploit)
✅ AIC (20%) = ALL CIA impact assessment (what happens if exploited)
✅ OT-specific = Your operational context drives the impact assessment
✅ Clean separation = CVSS C, I, A metrics are ignored, you assess them yourself

This approach allows you to:

• Accept CVSS scores from scanners (plug-and-play)
• Override IT-centric CIA assumptions with OT-specific AIC reality
• Produce accurate, defensible risk scores for OT environments

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How to Use the Calculator

Step-by-Step Guide

1️⃣ Enter Asset Information

Fill in the asset details:

• Asset Name/ID (required): Unique identifier (e.g., "PLC-REACTOR-01")
• Asset Type (required): PLC, SCADA, HMI, DCS, SIS, etc.
• Vulnerability Name (optional): Name or description of the vulnerability
• CVE ID (optional): If assessing a specific CVE
• Assessment Date (optional): When the assessment is being performed

2️⃣ Assess Each Dimension

Click the appropriate option box for each of the 6 dimensions. The calculator updates in real-time as you select options.

🚨 Dimension 1: Safety & Consequence Impact (30%)

Select the potential safety impact:

• None (0): No safety implications
• Minor (2.5): Minimal safety concern, no injury expected
• Moderate (5): Equipment damage possible, minor injuries possible
• Significant (7.5): Serious injury or environmental damage possible
• Catastrophic (10): Loss of life or major environmental disaster possible

⚠️ Safety Override: Selecting "Catastrophic" automatically ensures minimum score of 8.0

🔧 Dimension 2: Technical Vulnerability - Exploitability (15%)

This dimension measures exploitability only (how easy to exploit). Impact is assessed separately in AIC.

Choose your assessment method using the toggle buttons:

📊 CVSS Vector String (Recommended):

• Paste the full CVSS vector from your scanner
• Example: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Calculator extracts only AV, AC, PR, UI, S (exploitability)
• C, I, A values are ignored (you assess these in AIC dimension)

🔧 Manual Assessment:

• Use when no CVSS vector is available
• Answer five exploitability questions:
  • Attack Vector (Network/Adjacent/Local/Physical)
  • Attack Complexity (Low/High)
  • Privileges Required (None/Low/High)
  • User Interaction (None/Required)
  • Scope (Unchanged/Changed)
• Calculator computes exploitability score using CVSS 3.1 formula

📋 Note: This dimension measures exploitability only. The AIC dimension below is where you assess the actual operational impact.

🏭 Dimension 3: Asset Criticality & Role (20%)

What is the asset's role in operations?

• Support/Admin (2): Engineering workstation, development system
• Monitoring (5): HMI, historian, data collection only
• Production Control (7.5): Production PLC, SCADA master, process control
• Safety System (10): SIS, ESD, fire & gas system, safety PLC

🔐 Dimension 4: AIC Impact (20%)

How to use this dimension: This dimension is where you assess ALL operational impact for YOUR specific OT environment. The Technical dimension only measures exploitability, so this is where CIA impact is captured.

Why this matters:

• CVSS uses IT-centric CIA prioritization (Confidentiality first)
• OT environments prioritize AIC (Availability first)
• Same vulnerability can have vastly different operational impacts depending on asset role, network architecture, and compensating controls

Example: A CVSS 7.5 information disclosure vulnerability might score:

• IT System: High confidentiality impact (C:High)
• OT HMI (air-gapped): Low confidentiality impact (C:Low) - because the data exposed has minimal value in an isolated OT network

Assess impact on each component:

Availability Impact:

• None (0): No availability impact
• Low (3.33): Minor performance degradation
• Moderate (6.67): Significant downtime or service disruption
• High (10): Total loss of availability/shutdown required

Integrity Impact:

• None (0): No integrity impact
• Low (3.33): Limited data or control modification possible
• Moderate (6.67): Process control manipulation possible
• High (10): Full system compromise, unrestricted control modification

Confidentiality Impact:

• None (0): No confidentiality impact
• Low (3.33): Limited information disclosure
• Moderate (6.67): Sensitive operational data or IP exposure
• High (10): Complete data breach, trade secrets compromised

💡 OT Priority: Availability typically matters most in OT, followed by Integrity, then Confidentiality (opposite of IT's CIA priority!)

🛡️ Dimension 5: Environmental Context & Compensating Controls (10%)

What protections are in place?

• No Protection (10): Internet-facing, no network segmentation
• Basic Protection (7.5): Minimal firewall, flat network topology
• Moderate Protection (5): Network segmentation implemented, basic monitoring
• Good Protection (2.5): Defense in depth, IDS/IPS, active monitoring, trained staff
• Strong Protection (0): Air-gapped, physical security, comprehensive controls

🎯 Dimension 6: Threat Intelligence & Exploitability (5%)

Is this vulnerability being actively exploited?

• Theoretical (0): No known exploit, theoretical vulnerability only
• PoC Exists (3.33): Proof of concept published, not weaponized
• Public Exploit (6.67): Working exploit publicly available (Metasploit, ExploitDB)
• Active Exploitation (10): Active exploitation in the wild or CISA KEV listed

3️⃣ Review Results

The calculator displays:

• Individual dimension scores
• Weighted contributions
• Final Score (0.0 - 10.0)
• Risk Rating (Critical/High/Medium/Low/Informational)
• Priority (NOW/NEXT/PLANNED/NEVER)
• Timeline for remediation
• Detailed Recommendations for action

4️⃣ Take Action

Based on the score:

Score	Rating	Priority	Timeline	Action
9.0-10.0	🔴 CRITICAL	NOW	0-24 hours	Emergency response, immediate mitigation
7.5-8.9	🟠 HIGH	NEXT	1-7 days	Urgent, schedule in next maintenance window
5.5-7.4	🟡 MEDIUM	NEXT	1-30 days	Standard priority, quarterly cycle
3.0-5.4	🟢 LOW	PLANNED	30-90 days	Planned, annual maintenance
0.0-2.9	🔵 INFO	NEVER	Informational	Document only, no action required

5️⃣ Export or Share

• 🖨️ Print Report: Generate PDF for documentation
• 💾 Export JSON: Save data for vulnerability management tools
• 🔗 Copy URL: Share assessment with team members
• 🔄 Reset: Start a new assessment

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Methodology

Scoring Formula

Final Score = (Safety × 0.30) + (Technical × 0.15) + (Asset × 0.20) + 
              (AIC_Avg × 0.20) + (Environment × 0.10) + (Threat × 0.05)

Where:
  AIC_Avg = (Availability + Integrity + Confidentiality) / 3
  Technical = Exploitability sub-score only (CIA impact excluded)

Weight Rationale

Dimension	Weight	Category	Justification
Safety	30%	Impact	Life safety is paramount in OT; potential for loss of life or environmental catastrophe
Technical	15%	Exploitability	Pure exploitability only (CIA removed) - how easy to exploit, not what happens
Asset	20%	Impact	Not all assets are equal; safety systems need more protection than workstations
AIC	20%	Impact	ALL operational CIA impact; OT-specific context matters more than generic CVSS
Environment	10%	Context	Compensating controls significantly reduce actual risk
Threat	5%	Exploitability	Knowing exploits exist is important but shouldn't dominate the score

Category Breakdown:

• Impact Dimensions: Safety (30%) + Asset (20%) + AIC (20%) = 70%
• Exploitability/Context: Technical (15%) + Environment (10%) + Threat (5%) = 30%

This 70/30 split reflects OT's focus on consequences over exploitability.

Safety Override Rule

IF Safety_Impact == Catastrophic (10.0) THEN
    Final_Score = MAX(Final_Score, 8.0)
END IF

This ensures that any vulnerability with catastrophic safety implications is automatically rated at least HIGH (8.0), even if other factors would suggest a lower score.

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Scoring Dimensions

Detailed Dimension Descriptions

1. Safety & Consequence Impact (30%)

This dimension captures the worst-case safety, environmental, and production consequences of successful exploitation.

Scoring Guide:

Score	Level	Description	Examples
0	None	No safety or production impact	Isolated monitoring system, no operational control
2.5	Minor	Minimal safety concern, brief production impact	Temporary loss of monitoring data, minor quality issues
5	Moderate	Equipment damage, production downtime	Motor burnout, batch loss, 4-24 hour outage
7.5	Significant	Serious injury possible, major environmental or production impact	Chemical release, serious worker injury, >24 hour outage
10	Catastrophic	Loss of life or major environmental disaster possible	Explosion, toxic release, worker fatality, environmental catastrophe

2. Technical Vulnerability - Exploitability (15%)

This dimension measures exploitability only - how easy the vulnerability is to exploit. Impact (CIA) is assessed separately in the AIC dimension to avoid double-counting.

Two Assessment Methods:

📊 Method 1: CVSS Vector String (Recommended when available) Paste your CVSS vector string from the vulnerability scanner. The calculator extracts only exploitability metrics:

Metric	Extracted?	Description
AV (Attack Vector)	✅ Yes	Network / Adjacent / Local / Physical
AC (Attack Complexity)	✅ Yes	Low / High
PR (Privileges Required)	✅ Yes	None / Low / High
UI (User Interaction)	✅ Yes	None / Required
S (Scope)	✅ Yes	Unchanged / Changed (affects PR calculation)
C (Confidentiality)	❌ Ignored	Assessed in AIC dimension instead
I (Integrity)	❌ Ignored	Assessed in AIC dimension instead
A (Availability)	❌ Ignored	Assessed in AIC dimension instead

Example:

Input:  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Output: Exploitability Score = 10.0 (C:H, I:H, A:H ignored)

🔧 Method 2: Manual Assessment (When no CVSS available) Select values for each exploitability factor:

Factor	Options	CVSS Values
Attack Vector	Network (0.85), Adjacent (0.62), Local (0.55), Physical (0.2)	Higher = easier to exploit
Attack Complexity	Low (0.77), High (0.44)	Lower complexity = easier
Privileges Required	None (0.85), Low (0.62/0.68), High (0.27/0.50)	Values depend on Scope
User Interaction	None (0.85), Required (0.62)	No interaction = easier
Scope	Unchanged (U), Changed (C)	Affects PR values only

Exploitability Formula (CVSS 3.1):

Exploitability = 8.22 × AV × AC × PR × UI
Normalized Score = (Exploitability / 3.887) × 10

Why Scope Matters: Scope affects the Privileges Required calculation:

PR Level	Scope: Unchanged	Scope: Changed
None	0.85	0.85
Low	0.62	0.68
High	0.27	0.50

Key Point: This dimension is now pure exploitability - no overlap with AIC Impact.

3. Asset Criticality & Role (20%)

Not all assets are created equal in OT environments.

Scoring Guide:

Score	Asset Type	Description	Examples
2	Support/Admin	Non-operational support systems	Engineering workstations, development servers, corporate IT
5	Monitoring	Read-only monitoring and data collection	HMI (view only), historians, data loggers, reporting systems
7.5	Production Control	Direct process control, production operations	Production PLCs, SCADA masters, DCS controllers, VFDs
10	Safety System	Safety instrumented systems (SIS)	Safety PLCs, ESD systems, fire & gas systems, burner management

4. AIC Impact (15%)

Assessment of actual operational impact on Availability, Integrity, and Confidentiality in YOUR specific OT environment (OT-prioritized order).

Purpose: This dimension allows you to contextualize the generic CVSS impact for your specific operational reality. Unlike CVSS's IT-centric CIA scoring, this reflects actual OT consequences.

Why This Matters:

• CVSS assumes IT security priorities (Confidentiality > Integrity > Availability)
• OT environments have inverted priorities (Availability > Integrity > Confidentiality)
• Same vulnerability has vastly different operational impacts based on:
  • Asset role and criticality
  • Network architecture and isolation
  • Compensating controls
  • Operational context and redundancy

Availability Impact (Most Critical in OT):

Score	Level	Description	Operational Consequence
0	None	No availability impact	No operational disruption
3.33	Low	Minor performance degradation	Slight slowdown, no downtime
6.67	Moderate	Significant downtime or disruption	Hours of downtime, production impact
10	High	Total loss of availability/shutdown	Complete shutdown, emergency stop

Integrity Impact (Critical in OT):

Score	Level	Description	Operational Consequence
0	None	No integrity impact	Data and controls remain trustworthy
3.33	Low	Limited data/control modification	Minor parameter changes possible
6.67	Moderate	Process control manipulation possible	Setpoints, alarms, control logic at risk
10	High	Full system compromise	Complete control over process operations

Confidentiality Impact (Least Critical in OT, but still important):

Score	Level	Description	Operational Consequence
0	None	No confidentiality impact	No information disclosure
3.33	Low	Limited information disclosure	Process parameters, non-sensitive data
6.67	Moderate	Sensitive operational data exposed	Control strategies, operational secrets
10	High	Complete data breach/IP theft	Trade secrets, proprietary processes

Assessment Guidelines:

1. Consider YOUR specific environment, not generic assumptions
2. Factor in network isolation and compensating controls
3. Think about actual operational consequences, not theoretical impacts
4. Remember: In OT, a 10-hour production outage may be worse than a data leak

AIC Score Calculation:

AIC_Score = (Availability + Integrity + Confidentiality) / 3

5. Environmental Context & Controls (10%)

The security architecture and controls around the asset.

Scoring Guide:

Score	Level	Description
10	No Protection	Internet-facing, no firewall, flat network
7.5	Basic Protection	Basic firewall, flat OT network
5	Moderate Protection	Network segmentation, basic DMZ
2.5	Good Protection	Defense in depth, IDS/IPS, monitoring
0	Strong Protection	Air-gapped, physical security, 24/7 monitoring

6. Threat Intelligence & Exploitability (5%)

Real-world exploitation status and threat actor interest.

Scoring Guide:

Score	Level	Description
0	Theoretical	No known exploit
3.33	PoC Exists	Proof of concept published
6.67	Public Exploit	Working exploit publicly available
10	Active Exploitation	In-the-wild exploitation or CISA KEV

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Examples

Example 1: Safety PLC Vulnerability (Critical)

Scenario: Network-exploitable vulnerability in a safety PLC that controls emergency shutdown systems in a chemical plant. The system has basic segmentation but no IDS/IPS.

Assessment:

• Asset: Safety PLC (Emergency Shutdown System)
• Vulnerability: Remote Code Execution Vulnerability
• CVE: CVE-2024-12345
• CVSS Base Score: 9.8

Scoring:

Dimension	Selection	Score	Weighted
Safety & Consequence	Catastrophic - Chemical release possible	10.0	3.0 (30%)
Technical Vulnerability	Critical - CVSS 9.8, network RCE	10.0	2.0 (20%)
Asset Criticality	Safety System - ESD system	10.0	2.0 (20%)
AIC Impact	A:High, I:High, C:None	6.67	1.0 (15%)
Environment & Controls	Moderate - Basic segmentation	5.0	0.5 (10%)
Threat Intelligence	Public Exploit - Metasploit module exists	6.67	0.33 (5%)

Results:

• Final Score: 8.83
• Rating: 🔴 CRITICAL
• Priority: NOW (0-24 hours)
• Action: Emergency response required, implement workaround immediately, schedule emergency patch within 24 hours

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Example 2: Engineering Workstation (Low)

Scenario: Same CVE-2024-12345 vulnerability, but on an air-gapped engineering workstation used for occasional PLC programming.

Assessment:

• Asset: Engineering Workstation
• Vulnerability: Remote Code Execution Vulnerability
• CVE: CVE-2024-12345
• CVSS Base Score: 9.8 (same CVE)

Scoring:

Dimension	Selection	Score	Weighted
Safety & Consequence	None - No operational control	0.0	0.0 (30%)
Technical Vulnerability	Critical - CVSS 9.8, network RCE	10.0	2.0 (20%)
Asset Criticality	Support/Admin - Engineering workstation	2.0	0.4 (20%)
AIC Impact	A:None, I:Low, C:Moderate	3.33	0.5 (15%)
Environment & Controls	Strong - Air-gapped, physical security	0.0	0.0 (10%)
Threat Intelligence	Public Exploit - Metasploit module exists	6.67	0.33 (5%)

Results:

• Final Score: 3.23
• Rating: 🟢 LOW
• Priority: PLANNED (30-90 days)
• Action: Include in next annual maintenance, minimal urgency

Key Insight: Same CVE, dramatically different actual risk! CVSS would treat both identically (9.8), causing resource waste and operational disruption.

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Example 3: Production HMI with Good Controls (Medium)

Scenario: Moderate vulnerability (CVSS 6.5) in production HMI that monitors (but doesn't control) a manufacturing line. Good network segmentation and IDS in place.

Assessment:

• Asset: Production HMI (monitoring only)
• Vulnerability: Information Disclosure Vulnerability
• CVE: CVE-2024-67890
• CVSS Base Score: 6.5

Scoring:

Dimension	Selection	Score	Weighted
Safety & Consequence	Minor - Production visibility only	2.5	0.75 (30%)
Technical Vulnerability	Medium - CVSS 6.5, requires user interaction	5.0	1.0 (20%)
Asset Criticality	Monitoring - HMI, no control functions	5.0	1.0 (20%)
AIC Impact	A:Low, I:None, C:Low	2.22	0.33 (15%)
Environment & Controls	Good - Segmented, IDS/IPS, monitoring	2.5	0.25 (10%)
Threat Intelligence	PoC Exists - Research PoC only	3.33	0.17 (5%)

Results:

• Final Score: 3.50
• Rating: 🟢 LOW
• Priority: PLANNED (30-90 days)
• Action: Include in quarterly patch cycle, compensating controls adequate

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URL Parameters

Supported Parameters

The calculator supports pre-filling assessments via URL parameters, enabling integration with other tools and easy sharing.

Asset Information:

• asset - Asset name/ID
• type - Asset type
• vuln - Vulnerability name
• cve - CVE identifier
• date - Assessment date (YYYY-MM-DD format)

Dimension Scores:

• safety - Safety score (0, 2.5, 5, 7.5, 10)
• technical - Technical score (0, 3, 5, 7.5, 10)
• asset - Asset criticality (2, 5, 7.5, 10)
• availability - Availability impact (0, 3.33, 6.67, 10)
• integrity - Integrity impact (0, 3.33, 6.67, 10)
• confidentiality - Confidentiality impact (0, 3.33, 6.67, 10)
• environment - Environment score (0, 2.5, 5, 7.5, 10)
• threat - Threat score (0, 3.33, 6.67, 10)

Example URLs

1. Critical Safety PLC Assessment

OT_Risk_Calculator.html?asset=PLC-SAFETY-01&type=Safety+PLC&vuln=Remote+Code+Execution&cve=CVE-2024-12345&safety=10&technical=10&asset=10&availability=10&integrity=10&confidentiality=0&environment=5&threat=6.67

2. Low-Risk Engineering Workstation

OT_Risk_Calculator.html?asset=ENG-WS-05&type=Engineering+Workstation&vuln=RCE+Vulnerability&safety=0&technical=10&asset=2&availability=0&integrity=3.33&confidentiality=6.67&environment=0&threat=6.67

3. Medium-Risk HMI

OT_Risk_Calculator.html?asset=HMI-PROD-03&type=HMI&vuln=Information+Disclosure&cve=CVE-2024-67890&safety=2.5&technical=5&asset=5&availability=3.33&integrity=0&confidentiality=3.33&environment=2.5&threat=3.33

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Export & Integration

JSON Export Format

The calculator exports assessments in a standardized JSON format:

{
  "metadata": {
    "exportDate": "2024-11-19T10:30:00.000Z",
    "calculator": "OT Risk Severity Calculator",
    "assessmentDate": "2024-11-19"
  },
  "asset": {
    "name": "PLC-SAFETY-01",
    "type": "Safety PLC",
    "vulnerabilityName": "Remote Code Execution Vulnerability",
    "cveId": "CVE-2024-12345"
  },
  "dimensions": {
    "safety": 10.0,
    "technical": 10.0,
    "asset": 10.0,
    "aic": {
      "availability": 10.0,
      "integrity": 10.0,
      "confidentiality": 0.0
    },
    "environment": 5.0,
    "threat": 6.67
  },
  "results": {
    "finalScore": 8.83,
    "rating": "CRITICAL"
  }
}

Integration with Vulnerability Management Tools

Example: Import into Tenable.sc

import json
import requests

# Load OT Risk assessment
with open('ot_risk_assessment.json', 'r') as f:
    risk_data = json.load(f)

# Map to Tenable custom field
tenable_payload = {
    'cve': risk_data['asset']['cveId'],
    'asset': risk_data['asset']['name'],
    'custom_field_ot_risk_score': risk_data['results']['finalScore'],
    'custom_field_ot_risk_rating': risk_data['results']['rating']
}

# Send to Tenable API
requests.post('https://tenable.sc/api/vulnerability', json=tenable_payload)

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References

Standards & Frameworks

• IEC 62443 - Security for industrial automation and control systems
• NIST SP 800-82 - Guide to Industrial Control Systems (ICS) Security
• ISA/IEC 62443-3-2 - Security risk assessment for system design
• NERC CIP - Critical Infrastructure Protection standards
• ISO 27001/27019 - Information security management

CVSS References

• CVSS v3.1 Specification
• CVSS v4.0 Specification
• CVSS Calculator: https://www.first.org/cvss/calculator/

OT Security Resources

• ICS-CERT Advisories: https://www.cisa.gov/uscert/ics/advisories
• CISA Known Exploited Vulnerabilities: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• SANS ICS Security: https://www.sans.org/industrial-control-systems-security/

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