CVE 2021-39941

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

See the CVE page on Mitre.org for more details.