Wonka Slide <= 1.3.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode

The Wonka Slide plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's `list_class` shortcode in all versions up to, and including, 1.3.3 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.