The MP3 Audio Player WordPress plugin before 5.16 does not escape one of its audio player shortcode attributes before outputting it into an HTML attribute, allowing users with Contributor-level access and above to inject arbitrary JavaScript that executes when another user, such as an administrator previewing a pending post, views the content.
https://wpscan.com/vulnerability/b0013531-eecd-4cbc-a0d2-2872384e6f3c/