The dbus-daemon in D-Bus 1.2.x through 1.4.x, 1.6.x before 1.6.20, and 1.8.x before 1.8.4, sends an AccessDenied error to the service instead of a client when the client is prohibited from accessing the service, which allows local users to cause a denial of service (initialization failure and exit) or possibly conduct a side-channel attack via a D-Bus message to an inactive service.