When requests to the internal network for webhooks are enabled, a server-side request forgery vulnerability in GitLab CE/EE affecting all versions starting from 10.5 was possible to exploit for an unauthenticated attacker even on a GitLab instance where registration is limited
https://hackerone.com/reports/1110131
https://gitlab.com/gitlab-org/gitlab/-/issues/322926
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-22214.json