zot’s create-only policy allows overwrite attempts of existing latest tag (update permission not required) in zotregistry.dev/zot
zot’s create-only policy allows overwrite attempts of existing latest tag (update permission not required) in zotregistry.dev/zot. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: .
02 / AFFECTED SOFTWARE
Affected packages
87 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
zot is ancontainer image/artifact registry based on the Open Container Initiative Distribution Specification. From 1.3.0 to 2.1.14, zot’s dist-spec authorization middleware infers the required action for PUT /v2/{name}/manifests/{reference} as create by default, and only switches to update when the tag already exists and reference != "latest". As a result, when latest already exists, a user who is allowed to create (but not allowed to update) can still pass the authorization check for an overwrite attempt of latest. This vulnerability is fixed in 2.1.15.
zot’s dist-spec authorization middleware infers the required action for `PUT /v2/{name}/manifests/{reference}` as `create` by default, and only switches to `update` when the tag already exists and `reference != "latest"`. as a result, when `latest` already exists, a user who is allowed to `create` (but not allowed to `update`) can still pass the authorization check for an overwrite attempt of `latest`. ## affected component - file: `pkg/api/authz.go` (`DistSpecAuthzHandler`) - condition: `slices.Contains(tags, reference) && reference != "latest"` (line 352 at the pinned commit) ## severity HIGH category: CWE-863 (incorrect authorization) note: impact depends on how a deployment uses `latest` (for example, if `latest` is treated as a protected or “push-once” tag), and on how access control is provisioned (users with `create` but without `update`). the attached poc demonstrates a real overwrite of `latest` (tag digest changes) under a create-only policy. ## steps to reproduce 1. configure access control so user `attacker` has `create` but not `update` on a repository. 2. ensure the repository has an existing tag named `latest`. 3. attempt to push a new manifest to `/v2/acme/app/manifests/latest` (example repository name). 4. observe that the authorization check is evaluated as `create` (not `update`) for `latest`, so the request passes authorization even though the tag already exists. the attached poc demonstrates this deterministically with `canonical.log` and `control.log` markers. ## expected vs actual - expected: overwriting an existing tag should require `update` permission, including `latest` (or `latest` should be explicitly documented as exempt). - actual: when `reference=="latest"` and the tag exists, the middleware keeps the action as `create` instead of switching to `update`. ## security impact this can break least-privilege expectations in deployments that rely on the `create` vs `update` split to prevent tag overwrites (for example, “push-once” policies). if `latest` is used as a high-trust tag in ci/cd, this can create supply-chain risk because a create-only principal can overwrite an existing `latest` tag while other existing tags correctly require `update`. ## suggested fix remove the special-case exemption for `latest` when determining whether an existing tag requires `update` permission (treat `latest` the same as other tags), or document and enforce an explicit policy rule for `latest`. ## notes / rationale - oci distribution spec does not define a standard authorization model; this report is about zot’s own create vs update semantics and the observable behavior in `DistSpecAuthzHandler`. - zot documentation describes immutable tags as being enforceable via authorization policies (create-only “push once”, update disallowed). if `latest` is exempt, this control does not apply to `latest` unless documented otherwise. [addendum.md](https://github.com/user-attachments/files/24986139/addendum.md) [poc.zip](https://github.com/user-attachments/files/24986140/poc.zip) [PR_DESCRIPTION.md](https://github.com/user-attachments/files/24986141/PR_DESCRIPTION.md) [RUNNABLE_POC.md](https://github.com/user-attachments/files/24986142/RUNNABLE_POC.md)
zot’s create-only policy allows overwrite attempts of existing latest tag (update permission not required) in zotregistry.dev/zot. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: .
05 / REFERENCES