User Registration & Membership <= 5.1.4 - Missing Authorization to Authenticated (Contributor+) Limited Page Content Modification

The User Registration & Membership plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the `embed_form_action()` function in all versions up to, and including, 5.1.4. This makes it possible for authenticated attackers, with Contributor-level access and above, to append shortcode content to arbitrary pages they do not own or have permission to edit.