An information disclosure vulnerability in GitLab CE/EE versions 12.0 to 14.3.6, 14.4 to 14.4.4, and 14.5 to 14.5.2 allowed non-project members to see the default branch name for projects that restrict access to the repository to project members
https://hackerone.com/reports/706361
https://gitlab.com/gitlab-org/gitlab/-/issues/33864
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39941.json