An issue was discovered in GitLab Community and Enterprise Edition before 11.8.9. It has Incorrect Access Control. Unprivileged members of a project are able to post comments on confidential issues through an authorization issue in the note endpoint.
https://gitlab.com/gitlab-org/gitlab-ce/issues/58505
https://about.gitlab.com/2019/04/29/security-release-gitlab-11-dot-10-dot-2-released/