The AddFunc Head & Footer Code plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the aFhfc_head_code, aFhfc_body_code, and aFhfc_footer_code post meta values in all versions up to, and including, 2.3. This is due to the plugin outputting these meta values without any sanitization or escaping. While the plugin restricts its own metabox and save handler to administrators via current_user_can('manage_options'), it does not use register_meta() with an auth_callback to protect these meta keys. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts via the WordPress Custom Fields interface that execute when an administrator previews or views the post.