What Is Container Registry Security?

The registry is the distribution point for everything that runs in your environment, which makes it a supply chain control point disguised as storage. An attacker who can push to it does not need to compromise a cluster — the cluster will pull their image and run it on schedule.

It is treated as infrastructure plumbing in most organisations, with permissions granted broadly because pushing images is a routine developer activity.

Who can push is the central question

Read access can reasonably be broad. Write access should not be, and in practice it usually is — shared credentials used by several pipelines, long-lived tokens that never expire, and developer accounts able to push directly to the repositories production pulls from.

Separating the repositories that production consumes from the ones developers push to, with a promotion step between them, converts an open door into a controlled one. Promotion is also the natural place to require that an image has been scanned and signed.

Tags are not identity

A mutable tag can be repointed at different content at any time, so pulling a given tag today and tomorrow may produce different images with no record of the change. That is convenient for development and unacceptable for production.

Referencing images by immutable digest, or enforcing tag immutability in the registry, removes an entire class of quiet substitution. It also makes incident investigation possible, because the artefact that ran can be identified precisely rather than inferred.

Signing closes the loop

Scanning tells you an image was clean when it was examined. Signing tells you the image about to run is the one that was examined. Neither is sufficient alone: an unsigned scanned image can be substituted, and a signed unscanned image is merely authentically vulnerable.

Admission control is where both become enforcement. Without a policy refusing unsigned or unscanned images, signatures and scan results are records rather than controls.

Retention and the images you forgot

Registries accumulate. Every build produces an artefact, most are never deployed, and without a retention policy a registry ends up holding years of images — including ones with known vulnerabilities that anyone with pull access can still retrieve and run.

That matters more than storage cost suggests. An old image referenced by a forgotten deployment, a rollback that reaches for a two-year-old tag, or an attacker who simply pulls the most vulnerable version available all depend on those artefacts remaining accessible.

A retention policy that keeps tagged releases and expires untagged build artefacts after a short window removes most of it. Keeping the images that are genuinely deployable, and nothing else, also makes the scanning results mean something.

Registry availability is the operational risk that sits alongside the security one. If deployments and autoscaling both depend on pulling images, an unreachable registry prevents recovery at precisely the moment you need to scale or replace workloads — which is worth considering when the registry is a single external dependency.

Where to start

List the credentials with push access to the repositories production pulls from, and check which of them expire. Long-lived shared push credentials are the most common finding here and the most directly exploitable.

See supply chain security and container security. GuardsArm delivers cloud security assessment.