An issue was discovered in GitLab Community and Enterprise Edition 11.x before 11.3.11, 11.4.x before 11.4.8, and 11.5.x before 11.5.1. There is a persistent XSS vulnerability in the environment pages due to a lack of input validation and output encoding.
https://gitlab.com/gitlab-org/gitlab-ce/issues/53037
https://about.gitlab.com/2018/11/28/security-release-gitlab-11-dot-5-dot-1-released/