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.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:HA:H9.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:HAccess Control