SiteOrigin Widgets Bundle <= 1.70.4 - Missing Authorization to Authenticated (Subscriber+) Arbitrary Shortcode Execution

The SiteOrigin Widgets Bundle plugin for WordPress is vulnerable to unauthorized arbitrary shortcode execution in all versions up to, and including, 1.70.4. This is due to a missing capability check on the `siteorigin_widget_preview_widget_action()` function which is registered via the `wp_ajax_so_widgets_preview` AJAX action. The function only verifies a nonce (`widgets_action`) but does not check user capabilities. This makes it possible for authenticated attackers, with Subscriber-level access and above, to execute arbitrary shortcodes by invoking the `SiteOrigin_Widget_Editor_Widget` via the preview endpoint. The required nonce is exposed on the public frontend when the Post Carousel widget is present on a page, embedded in the `data-ajax-url` HTML attribute.