The Favorites plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'user_favorites' shortcode in all versions up to, and including, 2.3.3 due to insufficient input sanitization and output escaping on user supplied attributes such as 'no_favorites'. 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.