An issue has been discovered in GitLab CE/EE affecting all versions starting from 13.4. It was possible to exploit a stored cross-site-scripting in merge request via a specifically crafted branch name.
https://hackerone.com/reports/977697
https://gitlab.com/gitlab-org/gitlab/-/issues/254710
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-22196.json