The Kirki – Freeform Page Builder, Website Builder & Customizer plugin for WordPress is vulnerable to Stored Cross-Site Scripting via registration metadata in all versions up to, and including, 6.3.1 This is due to insufficient escaping in ExceptionalElements::image_element(), which concatenates a user-meta value straight into an <img src="…"> attribute. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute whenever a user accesses a page rendering a Kirki users collection whose image element is bound to one of the nine registration meta fields. Requires public user registration to be enabled and a published page carrying a kirki-register element, which prints the required element nonce into the public markup.