Waitlist Woocommerce ( Back in stock notifier ) <= 2.9.1 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'type' Shortcode Attribute

The Waitlist Woocommerce ( Back in stock notifier ) plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'type' Shortcode Attribute in all versions up to, and including, 2.9.1 due to insufficient input sanitization and output escaping. 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. The wp_kses_post filter applied on contributor post save does not prevent this vulnerability because shortcode attribute values are not HTML and pass through kses unchanged; the payload is materialized only at render time when the shortcode is expanded.