Implementing GCP Binary Authorization

Implementing GCP Binary Authorization

Overview

Binary Authorization is a Google Cloud deploy-time security control that ensures only trusted container images are deployed on GKE or Cloud Run. It works through a policy-based model where images must have cryptographic attestations confirming they passed predefined requirements such as vulnerability scans, code reviews, or build pipeline verification. Continuous validation (CV) monitors running pods against policies and logs violations.

When to Use

• When deploying or configuring implementing gcp binary authorization capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Common Misconfigurations & Verification

• Policy in dry-run / audit-only: an enforcementMode: DRYRUN_AUDIT_LOG_ONLY logs violations but deploys unattested images anyway. For real enforcement it must be ENFORCED_BLOCK_AND_AUDIT_LOG. Grep the exported policy for both enforcementMode and evaluationMode.
• evaluationMode: ALWAYS_ALLOW: this admits every image regardless of attestation, defeating the control. Production rules need REQUIRE_ATTESTATION (or ALWAYS_DENY as default).
• Overly broad whitelist patterns: admissionWhitelistPatterns like gcr.io/** or * bypass attestation entirely — keep them scoped to Google system images only.
• Binauthz not enabled on the cluster: the policy is org-wide but the cluster admits anything unless created/updated with --enable-binauthz.
• Break-glass without alerting: the break-glass: "true" label skips enforcement; without a log-based alert on it, it becomes a silent bypass.

gcloud container binauthz policy export | grep -E 'enforcementMode|evaluationMode|namePattern'
gcloud container clusters describe CLUSTER --zone ZONE \
  --format='value(binaryAuthorization.evaluationMode)'        # not DISABLED
# Negative test: an unattested image must be denied
kubectl run binauthz-test --image=docker.io/library/nginx:latest
kubectl get events --field-selector reason=FailedCreate

Prerequisites

• GCP project with Binary Authorization API enabled
• GKE cluster or Cloud Run service
• Container Analysis API enabled
• KMS keys for attestation signing
• Cloud Build or external CI/CD pipeline

Enable Binary Authorization

# Enable required APIs
gcloud services enable binaryauthorization.googleapis.com
gcloud services enable containeranalysis.googleapis.com
gcloud services enable container.googleapis.com

# Enable Binary Authorization on GKE cluster
gcloud container clusters update CLUSTER_NAME \
  --enable-binauthz \
  --zone us-central1-a

Create Attestor

Create a KMS key for signing

# Create keyring
gcloud kms keyrings create binauthz-keyring \
  --location global

# Create signing key
gcloud kms keys create attestor-key \
  --keyring binauthz-keyring \
  --location global \
  --algorithm ec-sign-p256-sha256 \
  --purpose asymmetric-signing

Create Container Analysis note

cat > /tmp/note.json << 'EOF'
{
  "attestation": {
    "hint": {
      "humanReadableName": "Production Build Attestor"
    }
  }
}
EOF

curl -X POST \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  "https://containeranalysis.googleapis.com/v1/projects/PROJECT_ID/notes/?noteId=prod-build-note" \
  -d @/tmp/note.json

Create the attestor

gcloud container binauthz attestors create prod-build-attestor \
  --attestation-authority-note=prod-build-note \
  --attestation-authority-note-project=PROJECT_ID

# Add KMS key to attestor
gcloud container binauthz attestors public-keys add \
  --attestor=prod-build-attestor \
  --keyversion-project=PROJECT_ID \
  --keyversion-location=global \
  --keyversion-keyring=binauthz-keyring \
  --keyversion-key=attestor-key \
  --keyversion=1

Configure Policy

Default deny-all policy

# binauthz-policy.yaml
admissionWhitelistPatterns:
  - namePattern: "gcr.io/google_containers/*"
  - namePattern: "gcr.io/google-containers/*"
  - namePattern: "k8s.gcr.io/**"
  - namePattern: "gke.gcr.io/**"
  - namePattern: "gcr.io/stackdriver-agents/*"
defaultAdmissionRule:
  evaluationMode: REQUIRE_ATTESTATION
  enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
  requireAttestationsBy:
    - projects/PROJECT_ID/attestors/prod-build-attestor
globalPolicyEvaluationMode: ENABLE

gcloud container binauthz policy import binauthz-policy.yaml

Per-cluster rules

admissionWhitelistPatterns:
  - namePattern: "gcr.io/google_containers/*"
clusterAdmissionRules:
  us-central1-a.production-cluster:
    evaluationMode: REQUIRE_ATTESTATION
    enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
    requireAttestationsBy:
      - projects/PROJECT_ID/attestors/prod-build-attestor
  us-central1-a.staging-cluster:
    evaluationMode: ALWAYS_ALLOW
    enforcementMode: DRYRUN_AUDIT_LOG_ONLY
defaultAdmissionRule:
  evaluationMode: ALWAYS_DENY
  enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG

Create Attestations

Attest an image after successful build

# Get image digest
IMAGE_DIGEST=$(gcloud container images describe \
  gcr.io/PROJECT_ID/my-app:latest \
  --format='get(image_summary.digest)')

# Create attestation
gcloud container binauthz attestations sign-and-create \
  --artifact-url="gcr.io/PROJECT_ID/my-app@${IMAGE_DIGEST}" \
  --attestor="prod-build-attestor" \
  --attestor-project="PROJECT_ID" \
  --keyversion-project="PROJECT_ID" \
  --keyversion-location="global" \
  --keyversion-keyring="binauthz-keyring" \
  --keyversion-key="attestor-key" \
  --keyversion="1"

Cloud Build integration

# cloudbuild.yaml
steps:
  - name: 'gcr.io/cloud-builders/docker'
    args: ['build', '-t', 'gcr.io/$PROJECT_ID/my-app:$SHORT_SHA', '.']

  - name: 'gcr.io/cloud-builders/docker'
    args: ['push', 'gcr.io/$PROJECT_ID/my-app:$SHORT_SHA']

  # Vulnerability scanning
  - name: 'gcr.io/cloud-builders/gcloud'
    entrypoint: 'bash'
    args:
      - '-c'
      - |
        gcloud artifacts docker images scan \
          gcr.io/$PROJECT_ID/my-app:$SHORT_SHA \
          --format='value(response.scan)'

  # Create attestation after successful scan
  - name: 'gcr.io/cloud-builders/gcloud'
    entrypoint: 'bash'
    args:
      - '-c'
      - |
        IMAGE_DIGEST=$(gcloud container images describe \
          gcr.io/$PROJECT_ID/my-app:$SHORT_SHA \
          --format='get(image_summary.digest)')
        gcloud container binauthz attestations sign-and-create \
          --artifact-url="gcr.io/$PROJECT_ID/my-app@$${IMAGE_DIGEST}" \
          --attestor="prod-build-attestor" \
          --attestor-project="$PROJECT_ID" \
          --keyversion-project="$PROJECT_ID" \
          --keyversion-location="global" \
          --keyversion-keyring="binauthz-keyring" \
          --keyversion-key="attestor-key" \
          --keyversion="1"

Continuous Validation

# Enable CV on a GKE cluster
gcloud container clusters update CLUSTER_NAME \
  --enable-binauthz-monitoring \
  --zone us-central1-a

Monitor CV violations in Cloud Logging

resource.type="k8s_cluster"
logName="projects/PROJECT_ID/logs/binaryauthorization.googleapis.com%2Fcontinuous_validation"

Verification and Testing

Test deployment of unattested image

# This should be blocked
kubectl run test-unapproved \
  --image=docker.io/library/nginx:latest

# Verify the pod was denied
kubectl get events --field-selector reason=FailedCreate

Verify attestation exists

gcloud container binauthz attestations list \
  --attestor=prod-build-attestor \
  --attestor-project=PROJECT_ID

Break-Glass Override

For emergency deployments bypassing Binary Authorization:

apiVersion: v1
kind: Pod
metadata:
  name: emergency-pod
  labels:
    image-policy.k8s.io/break-glass: "true"
  annotations:
    alpha.image-policy.k8s.io/break-glass: "Emergency deployment - ticket INC-12345"
spec:
  containers:
    - name: emergency
      image: gcr.io/PROJECT_ID/emergency-fix:latest

References

• GCP Binary Authorization: https://cloud.google.com/binary-authorization/docs
• SLSA Framework: https://slsa.dev
• Sigstore/Cosign for container signing
• Google Software Supply Chain Security Best Practices