The Feeds for YouTube (YouTube video, channel, and gallery plugin) plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'youtube-feed' shortcode in all versions up to, and including, 2.2.1 due to insufficient input sanitization and output escaping on user supplied attributes. 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.
https://plugins.trac.wordpress.org/changeset/3107577/
https://plugins.trac.wordpress.org/browser/feeds-for-youtube/trunk/js/sb-youtube.js