Feeds for YouTube <= 2.1 - Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode

The Feeds for YouTube plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'youtube-feed' shortcode in versions up to, and including, 2.1 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.