Layouts for WPBakery <= 1.1.3 - Missing Authorization to Unauthenticated Template Cache Manipulation via 'handle_sync' AJAX Action

The Layouts for WPBakery plugin for WordPress is vulnerable to unauthorized actions due to a missing capability check on the Layouts_WPB_Remote::template_sync() callback registered via wp_ajax_nopriv_handle_sync in all versions up to, and including, 1.1.3. This makes it possible for unauthenticated attackers to force the WordPress server to issue outbound HTTP requests to the plugin vendor's external API (https://www.layoutsforwpbakery.com/wp-json/layoutsforwpbakery/v1/{templates,categories}) and to write the JSON-decoded responses verbatim into the site's wp_options table via set_transient() — at any rate the attacker chooses, with no nonce verification, capability check, or rate limiting.