GitLab EE version 11.5 is vulnerable to a persistent XSS vulnerability in the Operations page. This is fixed in 11.5.1.
https://gitlab.com/gitlab-org/gitlab-ce/issues/53917
https://euvd.enisa.europa.eu/vulnerability/EUVD-2018-11268
https://about.gitlab.com/2018/11/28/security-release-gitlab-11-dot-5-dot-1-released/