PostX < 5.0.41 - Unauthenticated Custom Field Key Disclosure via REST API

The Post Grid Gutenberg Blocks WordPress plugin before 5.0.41 does not perform an authorization or post-visibility check on a REST API route that returns the custom field keys of a given post, allowing unauthenticated users to disclose the custom field key names of arbitrary posts, including private, draft, pending, scheduled and password-protected posts.