Securing Container Registry Images

agentic-workflows-blueprint.workflow.securing-container-registry-images

Goal

Secure container image registries by enforcing vulnerability scanning, image signing, SBOM traceability, and promotion gates that prevent unsafe artifacts from deployment.

Scope

• Applies to: image build/push/promotion controls in registries such as ECR, ACR, GCR/Artifact Registry, and equivalent platforms.
• Does not cover: runtime detection on deployed containers.

Triggers

• "Secure container registry images"
• "Require scan and signature before image promotion"
• "Implement SBOM and registry hardening controls"
• "Audit registry for unscanned/unsigned images"

Inputs

• registryPlatform: target registry provider(s)
• repositoryScope: repositories/tags/environments in scope
• severityPolicy: blocking thresholds for vulnerabilities
• signingModel: key-based or keyless signing approach
• sbomPolicy: required SBOM format and retention target
• promotionFlow: dev -> staging -> production image progression
• exceptionPolicy (optional): approved risk exceptions with expiry

Invariants

• Images must not be promoted to protected environments without passing scan policy.
• Image authenticity must be verifiable (signature and provenance expectations).
• Mutable tag risk must be controlled (immutability or digest-based promotion).
• SBOM and scan artifacts must be retained and linked to image digests.
• Exceptions must be explicit, reviewed, and time-bounded.

Procedure

1. Baseline registry security posture

   • Inventory repositories, scan settings, mutability rules, and retention policies.
   • Identify unscanned, unsigned, and high-risk images.

2. Enforce vulnerability scanning

   • Run Trivy and optional secondary scanner coverage (for example Grype) on target images.
   • Apply fail thresholds from severityPolicy.

3. Generate and persist SBOM

   • Generate SBOM artifacts (SPDX/CycloneDX) for promoted images.
   • Attach or store SBOM with immutable digest association.

4. Implement signing and verification

   • Sign images using configured signing model (keyed or keyless).
   • Verify signatures before promotion and/or admission.

5. Harden registry controls

   • Enable scan-on-push and tag immutability where supported.
   • Configure lifecycle and retention policies for hygiene.
   • Tighten registry IAM/RBAC access boundaries.

6. Integrate CI/CD promotion gate

   • Require scan + signature + SBOM checks before pushing/promoting release artifacts.
   • Block promotion on policy failures and emit remediation summary.

7. Continuous reassessment

   • Re-scan promoted artifacts on vulnerability DB updates.
   • Track drift between current findings and promotion-time status.

Outputs

• Registry security posture report with prioritized gaps.
• Scan artifacts and vulnerability summary per image digest.
• Signed image verification evidence and attestation metadata.
• SBOM inventory linked to promoted artifacts.
• Promotion gate report with pass/fail and exception details.

Review gate

• All promoted images pass vulnerability policy thresholds.
• Signature verification is enforced in promotion path.
• SBOM is generated and traceable to image digests.
• Tag immutability/digest controls prevent silent artifact replacement.
• Exceptions are documented with rationale, owner, and expiry.

References

• ../../SKILL.md
• ../scanning-docker-images-with-trivy/SKILL.md
• ../review/SKILL.md
• Interactive HTML View