An issue was discovered in GitLab Enterprise Edition 10.x (starting in 10.6) and 11.x before 11.5.8, 11.6.x before 11.6.6, and 11.7.x before 11.7.1. It has Incorrect Access Control. The merge request approvers section has an access control issue that permits project maintainers to view membership of private groups.
https://gitlab.com/gitlab-org/gitlab-ee/issues/8187
https://about.gitlab.com/2019/01/31/security-release-gitlab-11-dot-7-dot-3-released/