Moodle 2.x through 2.1.10, 2.2.x before 2.2.8, 2.3.x before 2.3.5, and 2.4.x before 2.4.2 allows remote authenticated administrators to obtain sensitive information from the external repositories of arbitrary users by leveraging the login_as feature.
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.