WooCommerce Multiple Free Gift <= 1.2.3 - Insufficient Server-Side Validation to Arbitrary Gift Adding

The WooCommerce Multiple Free Gift plugin for WordPress is vulnerable to gift manipulation in all versions up to, and including, 1.2.3. This is due to plugin not enforcing server-side checks on the products that can be added as a gift. This makes it possible for unauthenticated attackers to add non-gift items to their cart as a gift.