An issue has been discovered in GitLab affecting all versions starting from 14.0 before 14.0.9, all versions starting from 14.1 before 14.1.4, all versions starting from 14.2 before 14.2.2. The route for /user.keys is not restricted on instances with public visibility disabled. This allows user enumeration on such instances.
https://gitlab.com/gitlab-org/gitlab/-/issues/23832
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-22257.json