CVSS Score Extraction

Overview

CVSS (Common Vulnerability Scoring System) scores quantify vulnerability severity from 0-10. Different sources may provide different scores, requiring intelligent fallback handling.

Score Sources

NVD (National Vulnerability Database)

• Official US government vulnerability database
• Provides CVSS v3.0 and v3.1 scores
• Most comprehensive coverage
• URL pattern: https://nvd.nist.gov/vuln/detail/{CVE_ID}

GHSA (GitHub Security Advisory)

• GitHub's vulnerability advisory database
• Integrated with npm ecosystem
• URL pattern: https://github.com/advisories/{GHSA_ID}

RedHat Security

• RedHat-specific vulnerability data
• Often has additional context
• URL pattern: https://access.redhat.com/security/cve/{CVE_ID}

Source Priority

For optimal results, use this priority:

1. NVD CVSS v3.1 (most reliable, modern scoring)
2. NVD CVSS v3.0 (fallback, still reliable)
3. GHSA CVSS (GitHub advisory ecosystem)
4. RedHat CVSS (distribution-specific)
5. N/A (if no score available)

Data Extraction Pattern

def extract_cvss_score(vuln_data):
    """
    Extract CVSS score with source priority fallback.

    vuln_data: vulnerability object from Trivy or similar
    returns: (score, source) tuple
    """

    # Check NVD first (most authoritative)
    if 'nvd_cvss_v3_1' in vuln_data:
        return (vuln_data['nvd_cvss_v3_1'], 'NVD')

    if 'nvd_cvss_v3_0' in vuln_data:
        return (vuln_data['nvd_cvss_v3_0'], 'NVD')

    # Check GitHub Advisory
    if 'ghsa_cvss' in vuln_data:
        return (vuln_data['ghsa_cvss'], 'GHSA')

    # Check RedHat
    if 'redhat_cvss' in vuln_data:
        return (vuln_data['redhat_cvss'], 'RedHat')

    # No score available
    return ('N/A', 'Unknown')

Handling Missing Scores

When CVSS scores are unavailable:

def get_cvss_with_fallback(cve_id, vuln_sources):
    """
    Query multiple sources for CVSS score.

    cve_id: CVE identifier (e.g., CVE-2021-12345)
    vuln_sources: list of available data sources
    returns: (score_value, source_name)
    """

    for source in vuln_sources:
        score = source.get_cvss(cve_id)
        if score:
            return (score, source.name)

    # Fallback: use severity level as proxy
    return ('N/A', 'No Score Available')

Common Patterns

Trivy Integration

Trivy may not always include CVSS scores. For missing scores:

def enrich_with_cvss(trivy_results):
    """Enrich Trivy results with CVSS scores from NVD"""
    enriched = []

    for vuln in trivy_results:
        cve_id = vuln['VulnerabilityID']
        score = vuln.get('CVSS', {}).get('nvd', {}).get('V3Score', 'N/A')

        vuln['cvss_score'] = score
        enriched.append(vuln)

    return enriched

Usage

Use this skill when:

• Extracting CVSS scores from vulnerability data
• Need to prioritize scores from multiple sources
• Building vulnerability dashboards or reports
• Creating SLA-based remediation plans (based on CVSS severity)

Related Skills

• trivy-vulnerability-scanning: Source of vulnerability data
• security-audit-csv-reporting: Include CVSS scores in reports