Software Supply Chain Security: SBOM and SLSA Implementation

Software supply chain attacks have increased dramatically, targeting dependencies, build systems, and distribution channels. Software Bill of Materials (SBOM) and Supply-chain Levels for Software Artifacts (SLSA) provide frameworks for securing the software supply chain.

Supply Chain Attack Vectors

• Dependency Confusion: Malicious packages with internal names
• Typosquatting: Packages with similar names to popular ones
• Compromised Build Systems: Injecting malware during build
• Stolen Credentials: Publishing malicious updates

Generating SBOM with Syft

# Generate SBOM for container image
syft packages myapp:latest -o spdx-json > sbom.spdx.json

# Generate SBOM for source directory
syft dir:. -o cyclonedx-json > sbom.cyclonedx.json

# GitHub Actions integration
name: Generate SBOM
on: [push]

jobs:
  sbom:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - name: Generate SBOM
        uses: anchore/sbom-action@v0
        with:
          image: myapp:${{ github.sha }}
          format: spdx-json
          output-file: sbom.spdx.json
          
      - name: Upload SBOM
        uses: actions/upload-artifact@v3
        with:
          name: sbom
          path: sbom.spdx.json

SLSA Build Provenance

# GitHub Actions - SLSA Level 3 provenance
name: SLSA Build
on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    outputs:
      digest: ${{ steps.build.outputs.digest }}
    steps:
      - uses: actions/checkout@v4
      
      - name: Build and push
        id: build
        uses: docker/build-push-action@v5
        with:
          push: true
          tags: ghcr.io/org/app:${{ github.sha }}
          
  provenance:
    needs: build
    permissions:
      id-token: write
      contents: read
      actions: read
    uses: slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@v1.9.0
    with:
      image: ghcr.io/org/app
      digest: ${{ needs.build.outputs.digest }}
    secrets:
      registry-username: ${{ github.actor }}
      registry-password: ${{ secrets.GITHUB_TOKEN }}

Sigstore Signing

# Sign container image with Cosign
cosign sign --key cosign.key ghcr.io/org/app:v1.0.0

# Keyless signing with OIDC
cosign sign ghcr.io/org/app:v1.0.0

# Verify signature
cosign verify --key cosign.pub ghcr.io/org/app:v1.0.0

# Attach SBOM to image
cosign attach sbom --sbom sbom.spdx.json ghcr.io/org/app:v1.0.0

# Sign the SBOM
cosign sign --attachment sbom ghcr.io/org/app:v1.0.0

Kubernetes Policy Enforcement

# Kyverno policy - require signed images
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: verify-image-signature
spec:
  validationFailureAction: Enforce
  background: false
  rules:
  - name: verify-signature
    match:
      any:
      - resources:
          kinds:
          - Pod
    verifyImages:
    - imageReferences:
      - "ghcr.io/org/*"
      attestors:
      - entries:
        - keyless:
            subject: "https://github.com/org/*"
            issuer: "https://token.actions.githubusercontent.com"
            rekor:
              url: https://rekor.sigstore.dev

Dependency Lock Files

# Python - pip-tools for reproducible builds
pip-compile requirements.in --generate-hashes

# Node.js - npm with integrity
npm ci --ignore-scripts

# Go - verify checksums
go mod verify

# Renovate config for automated updates
{
  "extends": ["config:base"],
  "vulnerabilityAlerts": {
    "enabled": true
  },
  "packageRules": [
    {
      "matchUpdateTypes": ["patch", "minor"],
      "automerge": true
    }
  ]
}

Private Registry Security

# Terraform - ECR with scanning
resource "aws_ecr_repository" "app" {
  name                 = "app"
  image_tag_mutability = "IMMUTABLE"

  image_scanning_configuration {
    scan_on_push = true
  }

  encryption_configuration {
    encryption_type = "KMS"
    kms_key         = aws_kms_key.ecr.arn
  }
}

resource "aws_ecr_lifecycle_policy" "app" {
  repository = aws_ecr_repository.app.name

  policy = jsonencode({
    rules = [{
      rulePriority = 1
      description  = "Keep last 10 images"
      selection = {
        tagStatus   = "any"
        countType   = "imageCountMoreThan"
        countNumber = 10
      }
      action = {
        type = "expire"
      }
    }]
  })
}

Conclusion

Software supply chain security requires a multi-layered approach including SBOM generation, build provenance, artifact signing, and policy enforcement. By implementing SLSA practices and using tools like Sigstore, organizations can significantly reduce supply chain risks.