Elementor Website Builder <= 3.1.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via header_size

In the Elementor Website Builder WordPress plugin before 3.1.4, the heading widget (includes/widgets/heading.php) accepts a ‘header_size’ parameter. Although the element control lists a fixed set of possible html tags, it is possible for a user with Contributor or above permissions to send a modified ‘save_builder’ request with this parameter set to ‘script’ and combined with a ‘title’ parameter containing JavaScript, which will then be executed when the saved page is viewed or previewed.