Themify Builder <= 7.7.7 - Missing Authorization to Authenticated (Subscriber+) Arbitrary Post Stylesheet Write/Delete via tb_generate_on_fly AJAX Action

The Themify Builder plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 7.7.7. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with subscriber-level access and above, to overwrite or delete the generated CSS stylesheet file of arbitrary posts, including private and draft posts owned by other users, and modify plugin-scoped font options. The required CSRF nonce (tf_nonce) is emitted on public front-end builder pages via wp_localize_script, making it trivially obtainable by any authenticated user visiting such a page.