Sylius is an Open Source eCommerce Framework on Symfony. A cross-site scripting (XSS) vulnerability exists in the shop checkout login form handled by the ApiLoginController Stimulus controller. When a login attempt fails, AuthenticationFailureHandler returns a JSON response whose message field is rendered into the DOM using innerHTML, allowing any HTML or JavaScript in that value to be parsed and executed by the browser. The issue is fixed in versions: 2.0.16, 2.1.12, 2.2.3 and above.