Order Tip for WooCommerce <= 1.5.4 - Unauthenticated Tip Manipulation to Negative Value Leading to Unauthorized Discounts

The Order Tip for WooCommerce plugin for WordPress is vulnerable to Unauthenticated Improper Input Validation in all versions up to, and including, 1.5.4. This is due to lack of server-side validation on the `data-tip` attribute, which makes it possible for unauthenticated attackers to apply an excessive or even negative tip amount, resulting in unauthorized discount up to free orders depending on the value submitted.