Layouts for WPBakery < 1.1.4 - Missing Authorization to Unauthenticated Template Cache Manipulation via 'handle_sync' AJAX Action

Description

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.