Harden GitHub Actions Workflow - buildkit.yml

[int-stepsecurity-advanced]

GitHub Token Permissions Are Not Set to Minimum in Workflow

Summary

The GitHub token permissions in your workflow file (.github/workflows/buildkit.yml) exceed the minimum required. Reducing permissions to the minimum necessary enhances security by limiting the access scope of the token, thereby lowering the risk of accidental or malicious misuse.

Why This is Important

Using excessive permissions in GitHub workflows can expose your repository to potential security risks. The GitHub token grants access to repository resources, and any unnecessary permissions increase the likelihood of sensitive actions being performed without justification. By applying the principle of least privilege, you protect your repository from unintended data exposure and ensure that each job only has access to what it absolutely needs.

Evidence of Excessive Permissions

For more context, please refer to the build log from your recent workflow run, which highlights the permissions granted to the GitHub token that exceed the recommended minimum.

Suggested Fix

Below is the updated permissions configuration, which minimizes access for the GitHub token. Update your workflow file with this suggested configuration to resolve this issue:

```diff
  name: Publish Docker Image with buildkit
  on:
    workflow_dispatch:
  env:
    REGISTRY: ghcr.io
    IMAGE_NAME: ${{ github.repository }}
+ permissions:
+   contents: read
  jobs:
    build-and-push:
      runs-on: ubuntu-latest
      permissions:
        contents: read
        packages: write
      steps:
      - name: Harden Runner
        uses: step-security/harden-runner@int-sh
        with:
          egress-policy: audit
            
      - name: Checkout repository
        uses: actions/checkout@v4
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3
        with:
            buildkitd-flags: --debug
      - name: Log in to the Container registry
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Extract metadata (tags, labels) for Docker
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
      - name: Write docker file
        run: |
          # Create a Dockerfile that installs curl and makes outbound calls
          cat <<EOF > Dockerfile
          FROM ubuntu:latest
          RUN apt-get update && apt-get install -y curl
          EOF
            
      - name: Build and push Docker image
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=gha
          cache-to: type=gha,mode=max
          platforms: linux/amd64,linux/arm64
          provenance: true
          build-args: |
            BUILDKIT_INLINE_CACHE=1

Next Steps

Please review and update the workflow file with these minimum permissions. If additional permissions are necessary for certain steps, specify only those permissions explicitly.

For further guidance, refer to the GitHub documentation on fine-grained permissions.

Severity: High