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.

Cross-site scripting (XSS) vulnerability in flash/FlashMediaElement.as in MediaElement.js before 2.21.0, as used in WordPress before 4.5.2, allows remote attackers to inject arbitrary web script or HTML via an obfuscated form of the jsinitfunction parameter, as demonstrated by "jsinitfunctio%gn."

Cross-site scripting (XSS) vulnerability in flashmediaelement.swf in MediaElement.js before 2.11.2, as used in ownCloud Server 5.0.x before 5.0.5 and 4.5.x before 4.5.10, allows remote attackers to inject arbitrary web script or HTML via the file parameter.