The backend component in Open-Xchange OX App Suite before 7.6.3-rev36, 7.8.x before 7.8.2-rev39, 7.8.3 before 7.8.3-rev44, and 7.8.4 before 7.8.4-rev22 allows remote authenticated users to obtain sensitive information about external guest users via vectors related to the "groups" and "users" APIs.