The MediaElement.js WordPress plugin through 4.2.8 does not validate and escape some of its shortcode attributes before outputting them back in the page, which could allow users with a role as low as contributor to perform Stored Cross-Site Scripting attacks which could be used against high-privilege users such as admins.
https://wpscan.com/vulnerability/e57f38d9-889a-4f82-b20d-3676ccf9c6f9