Doco-CD has an OCI Trust Policy Bypass via Artifact-Contained Configuration

Summary

Doco-CD is a GitOps continuous delivery tool that automatically deploys and updates Docker Compose projects/services and Swarm stacks. Prior to version 0.90.1, a trust-boundary flaw in OCI artifact verification allowed artifact-provided deployment config to influence the policy used to verify that same artifact. When global OCI signature verification was enabled via `OCI_TRUST_POLICY` (`enabled: true`), an attacker with write access to the configured OCI tag could publish an unsigned or improperly signed artifact containing `.doco-cd.yml` with `oci.verify: false`. This could cause signature verification to be bypassed and untrusted deployment content to be applied. This primarily impacts users deploying from OCI artifacts where deployment config is read from artifact contents (for example, poll/webhook flows without trusted inline deployment overrides). The issue is fixed by enforcing a strict trust boundary and no-downgrade behavior. First, artifact-contained `.doco-cd.yml` is treated as untrusted for OCI trust-policy override decisions. Second, if global `OCI_TRUST_POLICY.enabled` is `true`, per-deployment `oci.verify: false` cannot disable verification. Some workarounds are available. Do not source deployment config from untrusted OCI artifact contents. Use trusted inline `POLL_CONFIG.deployments` and avoid relying on artifact-contained trust-policy overrides. Restrict write/push permissions for OCI repositories/tags used by doco-cd. Prefer immutable digest pinning and protected release/tag workflows. Monitor for unexpected artifact digest changes and failed/suspicious verification events.