CVE-2025-3889

The WordPress Simple Shopping Cart plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 5.1.3 via the ‘process_payment_data’ due to missing validation on a user controlled key. This makes it possible for unauthenticated attackers to change the quantity of a product to a negative number, which subtracts the product cost from the total order cost. The attack will only work with Manual Checkout mode, as PayPal and Stripe will not process payments for a negative quantity.

More information : https://plugins.trac.wordpress.org/browser/wordpress-simple-paypal-shopping-cart/tags/5.1.2/wp_shopping_cart.php#L324