An issue was discovered in GitLab Community and Enterprise Edition before 11.7.8, 11.8.x before 11.8.4, and 11.9.x before 11.9.2. It allows persistent XSS in the merge request "resolve conflicts" page.
https://about.gitlab.com/2019/04/01/security-release-gitlab-11-dot-9-dot-4-released/