OpenMage magento-lts before 20.19.0 and 21.0.0-beta1 before 21.0.0-beta3 contains a cross-site request forgery vulnerability in PayPal cancel and decline return handlers that trust only the checkout session without verifying the request came from PayPal. Attackers can lure a shopper into a cross-site GET to paypal/standard/cancel to cancel their recent uninvoiced order, void pending authorizations, and restore items to the cart.
CWE-352