Kudos Donations – Easy donations and payments with Mollie <= 3.2.9 - Reflected Cross-Site Scripting via 'add_query_arg'

The `Kudos Donations – Easy donations and payments with Mollie` plugin for WordPress is vulnerable to Reflected Cross-Site Scripting due to the use of `add_query_arg` without appropriate escaping on the URL in all versions up to, and including, 3.2.9. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute if they can successfully trick a user into performing an action, such as clicking on a specially crafted link.