The Presto Player plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'link_url' parameter of the [presto_player_overlay] shortcode in versions up to, and including, 4.2.0 This is due to insufficient input sanitization and output escaping in the getOverlays() function, which copies the link_url shortcode attribute directly into the overlay configuration without scheme validation, allowing javascript: URIs to survive and be rendered as the href of a clickable anchor element by the presto-dynamic-overlay-ui web component. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.