/way4acs/enroll in OpenWay WAY4 ACS before 1.2.278-2693 allows unauthenticated attackers to leverage response differences to discover whether a specific payment card number is stored in the system.
https://www.openwaygroup.com/way4-platform
https://gist.github.com/exviry/9527ce2ccdc0718d3ffd1e3ca62cf304