An issue was discovered in GitLab Community and Enterprise Edition 11.x before 11.3.11, 11.4.x before 11.4.8, and 11.5.x before 11.5.1. There is an incorrect access vulnerability that allows an unauthorized user to view private group names.
https://gitlab.com/gitlab-org/gitlab-ce/issues/51262
https://about.gitlab.com/2018/11/28/security-release-gitlab-11-dot-5-dot-1-released/