An issue has been discovered in GitLab CE/EE affecting all previous versions. If the victim is an admin, it was possible to issue a CSRF in System hooks through the API.
https://hackerone.com/reports/471274
https://gitlab.com/gitlab-org/gitlab/-/issues/26017
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-22202.json