AddFunc Head & Footer Code <= 2.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via Custom Fields

Summary

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.