The User.get method in Bugzilla/WebService/User.pm in Bugzilla 3.7.x and 4.0.x before 4.0.9, 4.1.x and 4.2.x before 4.2.4, and 4.3.x and 4.4.x before 4.4rc1 has a different outcome for a groups request depending on whether a group exists, which allows remote authenticated users to discover private group names by observing whether a call throws an error.