The GET /api/v1/user/actions/runners/registration-token endpoint (and its owner- and repository-level equivalents) creates a new runner registration token if none exists, yet the API scope middleware classifies it as read-only because it is a GET request. A holder of a leaked read:user-scoped token can therefore mint a registration token and register a malicious Actions runner that executes workflow jobs with access to repository secrets and source code.
Analyzing vulnerability vectors…