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supply-chain

Secure the software supply chain from source to running container. Covers Cosign keyless image signing (Sigstore/Rekor), SBOM generation and attestation (Syft), vulnerability scanning with severity gates (Trivy/Grype), SLSA Level 2 provenance, and Kyverno/OPA admission enforcement. All open-source, no license cost. Use when asked to "sign my image", "generate an SBOM", "scan for CVEs", "attest build provenance", "enforce image signatures in Kubernetes", or "implement SLSA".

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SKILL.md
Quality
Evals
Security

Secure the software supply chain — from the build pipeline to running containers.


Interactive Wizard (fires when no arguments are provided)

When invoked with no arguments, ask before proceeding:

Q1 — Mode?

What do you need?
  1. audit    — review an existing CI/CD pipeline for supply chain security gaps
  2. sign     — set up keyless image signing with Cosign (Sigstore/Rekor, no key management)
  3. sbom     — generate and attest an SBOM with Syft
  4. scan     — add a CVE vulnerability gate with Trivy or Grype
  5. enforce  — write a Kyverno policy to block unsigned images at admission
  6. slsa     — generate a SLSA Level 2 provenance workflow

Enter 1–6 or mode name:

Q2 — Context (after mode selected, one at a time):

  • audit: Paste your GitHub Actions workflow file(s) or describe your current CI/CD pipeline:
  • sign: Which container registry? (ECR / GHCR / Docker Hub / other):
  • sbom: Which image and registry? (e.g. ghcr.io/org/image):
  • scan: Which scanner preference? Trivy (recommended) or Grype — or no preference:
  • enforce: Which registry or image prefix should the policy cover? (e.g. ghcr.io/myorg/*):
  • slsa: Which registry and repo? (e.g. ghcr.io/org/image from github.com/org/repo):

Then proceed into the relevant mode below.


Mode: audit

Review an existing CI/CD pipeline and cluster admission configuration for supply chain security gaps.

Steps:

  1. Ask for or read: the GitHub Actions workflow file(s), any existing image scanning steps, and any Kyverno/OPA admission policies
  2. Classify gaps by severity:
    • Critical: images pushed without signing, no CVE gate, unsigned images admitted to cluster
    • High: SBOM not generated or not attested, severity gate only on CRITICAL (misses HIGH)
    • Medium: action versions pinned to tag not SHA, no SLSA provenance
  3. Output a prioritised gap list:
    [CRITICAL] No image signing — any image can be admitted to the cluster
    [CRITICAL] No CVE severity gate — vulnerable images pass CI
    [HIGH]     No SBOM attestation — cannot audit what is running
    [MEDIUM]   Action versions pinned to tag, not SHA
  4. Recommend the fix order: sign → scan-gate → SBOM → enforce → SLSA

Reference: references/supply-chain.md → Gap classification, Fix order

Mode: sign

Set up keyless image signing with Cosign using Sigstore/Rekor (no key management required).

Steps:

  1. Confirm the image registry (ECR, GHCR, Docker Hub) and CI platform (GitHub Actions assumed)
  2. Generate the signing workflow step:
    - name: Install Cosign
      uses: sigstore/cosign-installer@11086d9f32b178aa24e93c2b86eba3ef4b16b68a  # v3.8.1
    
    - name: Sign image
      run: |
        cosign sign --yes \
          ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build.outputs.digest }}
  3. Explain the keyless flow: GitHub Actions OIDC token → Fulcio CA → Rekor transparency log
  4. Show verification command:
    cosign verify \
      --certificate-identity-regexp="https://github.com/<org>/<repo>/.github/workflows/.*" \
      --certificate-oidc-issuer="https://token.actions.githubusercontent.com" \
      ghcr.io/<org>/<image>@<digest>
  5. Flag: always sign the digest (@sha256:…), never the tag — tags are mutable

Key rules:

  • Never store signing keys in CI secrets — use keyless only
  • Always sign the digest, not the tag
  • Pin cosign-installer to a full SHA, e.g.: sigstore/cosign-installer@11086d9f32b178aa24e93c2b86eba3ef4b16b68a

Reference: references/supply-chain.md → Keyless signing, Rekor transparency log

Mode: sbom

Generate a Software Bill of Materials with Syft and attest it as an OCI artifact alongside the image.

Steps:

  1. Add the SBOM generation step after build and push (digest is only available after registry push):
    - name: Generate SBOM
      uses: anchore/sbom-action@61119d458adab75f756bc0b9e4bde25725f86a7a  # v0.20.0
      with:
        image: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build.outputs.digest }}
        format: spdx-json
        output-file: sbom.spdx.json
    
    - name: Attest SBOM
      run: |
        cosign attest --yes \
          --predicate sbom.spdx.json \
          --type spdxjson \
          ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build.outputs.digest }}
  2. Show how to retrieve the SBOM attestation:
    cosign download attestation \
      --predicate-type https://spdx.dev/Document \
      ghcr.io/<org>/<image>@<digest> | jq '.payload | @base64d | fromjson'
  3. Note: use spdx-json format for broadest tooling compatibility; cyclonedx-json is an alternative

Reference: references/supply-chain.md → SBOM formats, Syft, Attestation

Mode: scan

Add a CVE vulnerability scan with a configurable severity gate that fails the build.

Steps:

  1. Add Trivy scan step:
    - name: Scan image for vulnerabilities
      uses: aquasecurity/trivy-action@18f2135c0b15d26b3a4c2efded75e06b6f0e4884  # v0.30.0
      with:
        image-ref: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build.outputs.digest }}
        format: table
        exit-code: '1'
        ignore-unfixed: true
        vuln-type: os,library
        severity: CRITICAL,HIGH
  2. Explain ignore-unfixed: true — skip CVEs with no fix available (reduces noise without reducing security)
  3. For Grype (alternative), show:
    - name: Scan with Grype
      uses: anchore/scan-action@e1165082ffb1fe366ebaf02d8526e7c4989ea9d2  # v7.4.0
      with:
        image: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build.outputs.digest }}
        fail-build: true
        severity-cutoff: high
  4. Recommend Trivy for new setups (CNCF, single binary, SBOM support); Grype for teams already using Syft

Reference: references/supply-chain.md → Trivy vs Grype, Severity gates

Mode: enforce

Generate a Kyverno ImageValidatingPolicy that blocks unsigned or unverified images at admission time.

Finding where unsigned images already run: Kubescape reports them as control C-0237 "Check if signature exists" (/platform-skills:kubescape-operator, or kubescape scan control C-0237 on a cluster). Use that list to size the rollout before switching the policy to Deny.

Steps:

  1. Ask: keyless (Sigstore) or key-based signing?
  2. For keyless, generate:
    apiVersion: policies.kyverno.io/v1
    kind: ImageValidatingPolicy
    metadata:
      name: require-signed-images
    spec:
      validationActions: [Audit]   # switch to [Deny] after all images are signing
      matchConstraints:
        resourceRules:
        - apiGroups: [""]
          apiVersions: ["v1"]
          operations: ["CREATE", "UPDATE"]
          resources: ["pods"]
      matchImageReferences:
      - glob: "ghcr.io/<org>/*"
      validations:
      - expression: >
          images.containers.map(image, verifyImageSignatures(image, [{"keyless": {
            "url": "https://fulcio.sigstore.dev",
            "rekor": {"url": "https://rekor.sigstore.dev"},
            "identities": [{"issuer": "https://token.actions.githubusercontent.com",
              "subjectRegExp": "https://github.com/<org>/.*"}]
          }}])).all(e, e > 0)
        message: "Image must be signed via Sigstore keyless signing from GitHub Actions"
  3. Show audit-first deployment:
    spec:
      validationActions: [Audit]   # start here, switch to [Deny] after validation
  4. Cross-reference: /platform-skills:kyverno for full ImageValidatingPolicy guidance

Reference: references/supply-chain.md → Kyverno enforcement, references/kyverno.md → ImageValidatingPolicy

Mode: slsa

Generate a GitHub Actions workflow for SLSA Level 2 provenance using slsa-github-generator.

Steps:

  1. Explain what SLSA L2 gives: signed provenance linking the artifact to the specific build inputs (source commit, workflow, runner)
  2. Generate the workflow using the official reusable workflow:
    jobs:
      build:
        runs-on: ubuntu-latest
        outputs:
          digest: ${{ steps.build.outputs.digest }}
        permissions:
          contents: read
          packages: write
        steps:
          - name: Build and push image
            id: build
            uses: docker/build-push-action@48aba3b46d1b1fec4febb7c5d0c644b249a11355  # v6.10.0
            with:
              push: true
              tags: ghcr.io/<org>/<image>:${{ github.sha }}
    
      provenance:
        needs: build
        permissions:
          actions: read
          id-token: write
          packages: write
        uses: slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@5a775b367a56d5bd118a224a811bba288150a563  # v2.0.0
        with:
          image: ghcr.io/<org>/<image>
          digest: ${{ needs.build.outputs.digest }}
          registry-username: ${{ github.actor }}
        secrets:
          registry-password: ${{ secrets.GITHUB_TOKEN }}
  3. Show provenance verification:
    slsa-verifier verify-image \
      ghcr.io/<org>/<image>@<digest> \
      --source-uri github.com/<org>/<repo> \
      --source-branch main
  4. Note: generator_container_slsa3.yml produces L2 provenance by default; L3 requires hermetic builds not available on standard GitHub-hosted runners

Reference: references/supply-chain.md → SLSA levels, slsa-github-generator


Signing and SBOMs cover what the pipeline produces. They say nothing about the pipeline itself — an unpinned uses: or a pull_request_target checkout of untrusted code compromises the build before any artifact exists. To audit the workflows that run this supply chain, including unpinned-uses hash-pin policy enforcement, use /platform-skills:zizmor. They also say nothing about whether a credential leaked into the repo that produces this artifact in the first place — for that, live-validate and revoke with /platform-skills:kingfisher.


After completing this task, log errors and learnings via /platform-skills:self-improve log.

Repository

nitinjain999/platform-skills

Path

skills/supply-chain/SKILL.md

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Also appears in

nitinjain999/platform-skills
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since Oct 19, 2026

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