Analyzing SBOM for Supply Chain Vulnerabilities

When to Use

• A new regulatory requirement (EO 14028, EU CRA) mandates SBOM analysis for software deliveries
• Security team needs to assess third-party risk by scanning vendor-provided SBOMs
• CI/CD pipeline requires automated vulnerability checks against generated SBOMs
• Incident response needs to determine if a newly disclosed CVE affects deployed software
• Procurement team requires supply chain risk assessment for a software acquisition

Do not use for runtime vulnerability scanning of live systems; use container scanning tools (Trivy, Grype CLI) or host-based vulnerability scanners (Nessus, Qualys) instead.

Prerequisites

• SBOM file in CycloneDX JSON (v1.4+) or SPDX JSON (v2.3+) format
• Python 3.9+ with requests, networkx, and packaging libraries installed
• NVD API key (free, from https://nvd.nist.gov/developers/request-an-api-key) for higher rate limits
• Network access to NVD API (https://services.nvd.nist.gov/rest/json/cves/2.0)
• Optionally: syft for SBOM generation, grype for cross-validation

Workflow

Step 1: Generate SBOM (if not provided)

Use syft to create an SBOM from a container image or project directory:

# Generate CycloneDX JSON from a container image
syft alpine:latest -o cyclonedx-json > sbom-cyclonedx.json

# Generate SPDX JSON from a project directory
syft dir:/path/to/project -o spdx-json > sbom-spdx.json

# Generate from a running container
syft docker:my-app-container -o cyclonedx-json > sbom.json

Syft supports over 30 package ecosystems including npm, PyPI, Maven, Go modules, apt, apk, and RPM. The generated SBOM includes package names, versions, licenses, CPE identifiers, and PURL (Package URL) references.

Step 2: Parse SBOM and Extract Components

Parse the SBOM to extract all software components with their identifiers:

CycloneDX JSON Structure:

{
  "bomFormat": "CycloneDX",
  "specVersion": "1.5",
  "components": [
    {
      "type": "library",
      "name": "lodash",
      "version": "4.17.20",
      "purl": "pkg:npm/lodash@4.17.20",
      "cpe": "cpe:2.3:a:lodash:lodash:4.17.20:*:*:*:*:*:*:*",
      "licenses": [{"license": {"id": "MIT"}}]
    }
  ],
  "dependencies": [
    {"ref": "pkg:npm/express@4.18.2", "dependsOn": ["pkg:npm/lodash@4.17.20"]}
  ]
}

SPDX JSON Structure:

{
  "spdxVersion": "SPDX-2.3",
  "packages": [
    {
      "name": "lodash",
      "versionInfo": "4.17.20",
      "externalRefs": [
        {"referenceType": "purl", "referenceLocator": "pkg:npm/lodash@4.17.20"},
        {"referenceType": "cpe23Type", "referenceLocator": "cpe:2.3:a:lodash:lodash:4.17.20:*:*:*:*:*:*:*"}
      ],
      "licenseConcluded": "MIT"
    }
  ],
  "relationships": [
    {"spdxElementId": "SPDXRef-express", "relatedSpdxElement": "SPDXRef-lodash",
     "relationshipType": "DEPENDS_ON"}
  ]
}

Step 3: Correlate Components with NVD CVE Database

Query the NVD 2.0 API to find known vulnerabilities for each component:

import requests

NVD_API = "https://services.nvd.nist.gov/rest/json/cves/2.0"

def search_cves_by_cpe(cpe_name, api_key=None):
    params = {"cpeName": cpe_name, "resultsPerPage": 50}
    headers = {"apiKey": api_key} if api_key else {}
    resp = requests.get(NVD_API, params=params, headers=headers, timeout=30)
    resp.raise_for_status()
    return resp.json().get("vulnerabilities", [])

def search_cves_by_keyword(keyword, version=None, api_key=None):
    params = {"keywordSearch": keyword, "resultsPerPage": 50}
    headers = {"apiKey": api_key} if api_key else {}
    resp = requests.get(NVD_API, params=params, headers=headers, timeout=30)
    resp.raise_for_status()
    return resp.json().get("vulnerabilities", [])

The NVD API supports searching by CPE name (most precise), keyword, CVE ID, and date ranges. Rate limits: 5 requests/30 seconds without API key, 50 requests/30 seconds with key.

Step 4: Build Dependency Graph and Identify Transitive Risks

Construct a directed graph of dependencies to trace vulnerability propagation:

import networkx as nx

def build_dependency_graph(sbom):
    G = nx.DiGraph()
    # Add nodes for each component
    for comp in sbom["components"]:
        G.add_node(comp["purl"], name=comp["name"], version=comp["version"])
    # Add edges from dependency relationships
    for dep in sbom.get("dependencies", []):
        for child in dep.get("dependsOn", []):

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