An issue has been discovered in GitLab affecting all versions starting from 15.9 before 15.9.4, all versions starting from 15.10 before 15.10.1. It was possible for an unauthorised user to add child epics linked to victim's epic in an unrelated group.
https://hackerone.com/reports/1892200
https://gitlab.com/gitlab-org/gitlab/-/issues/396720
https://gitlab.com/gitlab-org/cves/-/blob/master/2023/CVE-2023-1417.json