Meta Box AIO <= 3.8.0 - Missing Authorization to Unauthenticated Arbitrary Post Deletion via 'rwmb_frontend_field_object_id' Parameter

The Meta Box AIO plugin for WordPress is vulnerable to Missing Authorization via the template_redirect dispatcher in the MB Frontend Submission extension in versions up to, and including, 3.8.0. This is due to the handle_request() function routing the mbfs_delete action without any capability or ownership check, and the nonce verification in check_ajax() being gated behind is_ajax() which is false for template_redirect requests, making it bypassable. This makes it possible for unauthenticated attackers to delete arbitrary posts and pages by supplying an attacker-controlled post ID via the rwmb_frontend_field_object_id GET parameter on any page that hosts a frontend submission form regardless of whether allow_delete is enabled.