shop.redbullmobile.at XSS vulnerability

Vulnerable URL: http://shop.redbullmobile.at/is-bin/INTERSHOP.enfinity/WFS/Mobilkom-A1Shop-Site/deAT/-/EUR/CouponHandlingView-AddCoupon?submitcouponID=Einl%c3%b6sen=alle-handys=OverviewPage=Gutscheincode%2520eingebenalert/XSSPOSED/...