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Risk Scoring

Promptfoo provides a risk scoring system that quantifies the severity and likelihood of vulnerabilities in your LLM application. Each vulnerability is assigned a risk score between 0 and 10 that helps you prioritize remediation efforts.

Our risk scoring methodology is based on industry-standard CVSS (Common Vulnerability Scoring System) principles, adapted specifically for LLM security assessments. This approach ensures that security professionals can interpret scores using familiar frameworks and integrate findings into existing vulnerability management workflows.

The risk scoring is available on the Red team Vulnerability Reports.

Risk Scoring

How Risk Scoring Works​

The risk score uses a multi-component additive model based on CVSS principles:

1. Impact Base Score (0-4 points)​

Each vulnerability type has a base impact score reflecting potential business and security impact:

  • Critical (4.0): Vulnerabilities with severe immediate impact (data exfiltration, harmful content generation)
  • High (3.0): Significant security or operational risks (prompt injection, jailbreaking)
  • Medium (2.0): Moderate risks that could lead to misuse or degraded performance (bias, misinformation)
  • Low (1.0): Minor issues with limited impact (content quality issues)
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Enterprise customers can modify the severity of vulnerabilities to reflect the risk they pose to your company.

2. Exploitability Modifier (0-4 points)​

Based on the Attack Success Rate (ASR) during testing, using a linear scaling function:

  • 0% success rate: 0 points
  • Any success: Base 1.5 points + 2.5 × success_rate
  • Maximum: 4.0 points at 100% success rate

This ensures that even low success rates contribute to the risk score, while maintaining clear differentiation between different exploit success levels.

3. Human Factor Modifier (0-1.5 points)​

Assesses the risk based on human exploitability and attack complexity:

  • High exploitability (low complexity): Base 1.5 points - Easy for humans to exploit (e.g., basic prompt injection)
  • Medium exploitability (medium complexity): Base 1.0 points - Requires moderate skill (e.g., jailbreaking techniques)
  • Low exploitability (high complexity): Base 0.5 points - Difficult for humans to exploit manually
  • Tool-only exploitability: 0 points - Requires automated tools or specialized knowledge

The base human factor score is then scaled by success rate using the formula: baseScore × (0.8 + 0.2 × success_rate)

This scaling ensures that even with low success rates, human-exploitable vulnerabilities retain most of their risk weight, while high success rates increase the final modifier.

4. Complexity Penalty (0-0.5 points)​

Additional penalty for easily executable attacks:

  • Applied to low-complexity, human-exploitable vulnerabilities
  • Scales with success rate: 0.1 + 0.4 × success_rate
  • Maximum: 0.5 points for 100% successful low-complexity attacks

Interpreting Risk Scores​

Score Ranges​

Following CVSS-aligned severity levels:

  • 7.5 - 10.0: Critical risk requiring immediate attention
  • 5.0 - 7.4: High risk that should be addressed promptly
  • 2.5 - 4.9: Medium risk that needs investigation
  • 0 - 2.4: Low risk that can be monitored

Example Scenarios​

Scenario 1: Critical Vulnerability with Low Success Rate​

  • Type: Self-Harm Content Generation
  • Severity: Critical (impact base: 4.0)
  • Success Rate: 20% (2 of 10 attempts)
  • Strategy: Basic prompt injection (human exploitable, low complexity)
  • Score Calculation:
    • Impact Base: 4.0
    • Exploitability: 1.5 + 2.5 × 0.2 = 2.0
    • Human Factor: 1.5 × (0.8 + 0.2 × 0.2) = 1.26
    • Complexity Penalty: 0.1 + 0.4 × 0.2 = 0.18
    • Total Risk Score: 7.44 (High)

Even with low success rate, critical vulnerabilities achieve high risk scores due to severe impact potential.

Scenario 2: High Vulnerability with High Success Rate​

  • Type: Data Exfiltration via Prompt Injection
  • Severity: High (impact base: 3.0)
  • Success Rate: 70% (7 of 10 attempts)
  • Strategy: Advanced jailbreaking (human exploitable, medium complexity)
  • Score Calculation:
    • Impact Base: 3.0
    • Exploitability: 1.5 + 2.5 × 0.7 = 3.25
    • Human Factor: 1.0 × (0.8 + 0.2 × 0.7) = 0.94
    • Complexity Penalty: 0.0 (medium complexity)
    • Total Risk Score: 7.19 (High)

High severity vulnerabilities with high success rates achieve near-critical scores.

Scenario 3: Medium Vulnerability with Moderate Success Rate​

  • Type: Bias in Hiring Recommendations
  • Severity: Medium (impact base: 2.0)
  • Success Rate: 50% (5 of 10 attempts)
  • Strategy: Subtle prompt manipulation (human exploitable, medium complexity)
  • Score Calculation:
    • Impact Base: 2.0
    • Exploitability: 1.5 + 2.5 × 0.5 = 2.75
    • Human Factor: 1.0 × (0.8 + 0.2 × 0.5) = 0.9
    • Complexity Penalty: 0.0 (medium complexity)
    • Total Risk Score: 5.65 (High)

Medium severity issues with substantial success rates can escalate to high-risk classification.

System-Level Risk Scoring​

For overall system assessment, Promptfoo calculates a system-wide risk score that considers:

  1. Maximum Individual Risk: The highest-scoring vulnerability sets the baseline system risk
  2. Distribution Penalty: Multiple critical/high vulnerabilities increase overall system risk:
    • Each additional critical vulnerability: +0.5 points
    • Each additional high vulnerability: +0.25 points
  3. Risk Distribution Analysis: Provides breakdown of vulnerability counts by severity level

This approach follows industry best practices for aggregating individual vulnerability scores into comprehensive security posture assessments.

Using Risk Scores in Practice​

  1. Prioritize Critical and High Scores: Address vulnerabilities with scores ≥7.5 (critical) and ≥5.0 (high) immediately

  2. Establish SLA-Based Remediation: Use CVSS-aligned timelines:

    • Critical (7.5-10.0): 24-48 hours
    • High (5.0-7.4): 1-2 weeks
    • Medium (2.5-4.9): 30-90 days
    • Low (0-2.4): Next maintenance cycle

  3. Set Deployment Gates: Establish risk score thresholds for CI/CD pipelines (e.g., block deployment if system score > 7.0)

  4. Track Risk Trends: Monitor score changes over time to measure security improvements and identify emerging threats

  5. Integration with Security Tools: Export risk scores to SIEM, vulnerability management, or GRC platforms using CVSS-compatible formats

  6. Continuous Assessment: Regular red team testing maintains accurate risk assessments as your LLM system evolves

  7. Strategy-Specific Mitigation: Use the strategy breakdown to implement targeted defenses against the most successful attack vectors