The Hyland Onbase Application Server releases prior to 20.3.58.1000 and OnBase releases 21.1.1.1000 through 21.1.15.1000 are vulnerable to a username enumeration vulnerability. An attacker can obtain valid users based on the response returned for invalid and valid users by sending a POST login request to the /mobilebroker/ServiceToBroker.svc/Json/Connect endpoint. This can lead to user enumeration against the underlying Active Directory integrated systems.