sbom-supply-chain

name	sbom-supply-chain
type	skill
description	Generate, attach, and verify SBOMs (CycloneDX/SPDX) for container images; implement SLSA provenance; harden software supply chain.
related-rules	["supply-chain-security.md (ci-cd)","shift-left-policy.md"]
allowed-tools	Read, Write, Edit, Bash

Skill: SBOM & Supply Chain Security

Expertise: Syft/Trivy SBOM generation, cosign SBOM attestation, SLSA provenance, dependency pinning, OCI attestations.

When to load

When generating SBOMs for images, attaching attestations to OCI registry, verifying supply chain integrity, or achieving SLSA compliance.

SBOM Generation (Syft)

# Generate CycloneDX SBOM from image (OCI)
syft registry.example.com/myorg/order-service:v1.2.3 \
  -o cyclonedx-json=sbom.cdx.json

# Generate SPDX SBOM from image
syft registry.example.com/myorg/order-service:v1.2.3 \
  -o spdx-json=sbom.spdx.json

# Generate from local directory (during build)
syft dir:. -o cyclonedx-json=sbom.cdx.json

# Generate from Dockerfile build context (before push)
syft packages docker:myimage:latest -o cyclonedx-json=sbom.cdx.json

SBOM Attestation via cosign

# Sign image and attach SBOM as OCI attestation
# Step 1: Build and push image
docker buildx build --push \
  -t registry.example.com/myorg/order-service:v1.2.3 .

# Step 2: Get digest
DIGEST=$(crane digest registry.example.com/myorg/order-service:v1.2.3)

# Step 3: Generate SBOM
syft registry.example.com/myorg/order-service:v1.2.3 \
  -o cyclonedx-json=sbom.cdx.json

# Step 4: Attach SBOM as attestation (Sigstore keyless)
cosign attest \
  --predicate sbom.cdx.json \
  --type cyclonedx \
  registry.example.com/myorg/order-service@${DIGEST}

# Step 5: Verify attestation exists
cosign verify-attestation \
  --type cyclonedx \
  --certificate-identity-regexp ".*" \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  registry.example.com/myorg/order-service@${DIGEST} \
  | jq '.payload | @base64d | fromjson | .predicate.metadata'

GitHub Actions: Full Supply Chain Pipeline

# .github/workflows/supply-chain.yml
jobs:
  build-sign-attest:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      packages: write
      id-token: write         # for cosign keyless signing

    steps:
      - uses: actions/checkout@v4

      - name: Install cosign
        uses: sigstore/cosign-installer@v3

      - name: Install syft
        uses: anchore/sbom-action/download-syft@v0

      - name: Build and push
        id: build
        uses: docker/build-push-action@v6
        with:
          push: true
          tags: registry.example.com/myorg/order-service:${{ github.sha }}

      - name: Sign image (keyless via OIDC)
        run: |
          cosign sign \
            registry.example.com/myorg/order-service@${{ steps.build.outputs.digest }}

      - name: Generate SBOM
        run: |
          syft registry.example.com/myorg/order-service@${{ steps.build.outputs.digest }} \
            -o cyclonedx-json=sbom.cdx.json

      - name: Attach SBOM attestation
        run: |
          cosign attest \
            --predicate sbom.cdx.json \
            --type cyclonedx \
            registry.example.com/myorg/order-service@${{ steps.build.outputs.digest }}

      - name: Generate SLSA provenance
        uses: slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@v2
        with:
          image: registry.example.com/myorg/order-service
          digest: ${{ steps.build.outputs.digest }}

Verify Before Deploy (admission check)

# Verify image is signed before deploying
cosign verify \
  --certificate-identity-regexp "https://github.com/myorg/myrepo" \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  registry.example.com/myorg/order-service@sha256:<digest>

# Kyverno policy: enforce signed images in production
# (see opa-policies skill for full Kyverno policy)

Dependency Pinning (supply chain hardening)

# Pin base image to digest — not just tag
FROM python:3.12-slim@sha256:abc123...   # ✅
FROM python:3.12-slim                    # ❌ tag can be replaced

# Verify base image digest in CI
crane digest python:3.12-slim

# Python: generate requirements with hashes (pip-compile)
pip-compile --generate-hashes requirements.in -o requirements.txt

# Install with hash verification
pip install -r requirements.txt --require-hashes

# Node: lock file with integrity hashes (automatic in npm/yarn)
npm ci   # uses package-lock.json with sha512 integrity hashes

SBOM Analysis

# Scan SBOM for vulnerabilities (without re-pulling image)
grype sbom:sbom.cdx.json --fail-on high

# List all packages in SBOM
cat sbom.cdx.json | jq '.components[] | {name: .name, version: .version, purl: .purl}'

# Check for GPL licenses in SBOM
cat sbom.cdx.json | jq '.components[] | select(.licenses[]?.license.id | startswith("GPL"))'