Magazine Blocks <= 1.8.6 - Missing Authorization to Authenticated (Contributor+) Arbitrary Post Modification / Site-Wide Template Takeover via Builder Templates REST Endpoint

The Magazine Blocks – Blog Designer, Magazine & Newspaper Website Builder, Page Builder with Posts Blocks, Post Grid plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 1.8.6. 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 contributor-level access and above, to demote administrator-owned published builder templates (header, footer, front page, single, archive, 404, and search) to draft status and replace them with attacker-authored block content rendered site-wide, enabling defacement, phishing, and SEO spam. This is possible because the mzb-builder-template post type is registered with capability_type='post' and exposed via the REST API, and the _mzb_template meta key is accessible to any user with edit_posts capability, meaning Contributor-level users and above can trigger the vulnerable save_post() hook.