Images are signed using Docker Content Trust or Cosign; verification enforced at deployment

Unsigned container images can be silently replaced in a registry — an attacker who gains push access to a registry can swap a legitimate image for a malicious one with the same tag, and every subsequent deployment pulls the compromised image without any cluster-level detection (CWE-494, NIST 800-53 CM-14, SLSA L3). Image signing with Cosign or Docker Content Trust creates a cryptographically verifiable chain from the image back to the CI system that built it. SSDF 800-218 PS.2.1 requires build provenance. Without admission webhook enforcement, signing alone is advisory — images can still be deployed without verification.

Sign images during CI/CD with Cosign and enforce verification at admission. In .github/workflows/build.yml:

# Generate key pair once, store private key as CI secret
cosign generate-key-pair

# Sign after push
cosign sign --key cosign.key $IMAGE_REF

Store COSIGN_PRIVATE_KEY and COSIGN_PASSWORD as CI secrets. The public key (cosign.pub) is committed to the repository. For enforcement, deploy Sigstore's policy-controller and create a ClusterImagePolicy referencing your public key — this blocks admission of any pod whose image digest cannot be verified against the policy.