An issue was discovered in GitLab Community and Enterprise Edition before 11.8.9, 11.9.x before 11.9.10, and 11.10.x before 11.10.2. It has Improper Encoding or Escaping of Output. The branch name on new merge request notification emails isn't escaped, which could potentially lead to XSS issues.
https://gitlab.com/gitlab-org/gitlab-ee/issues/11515
https://about.gitlab.com/2019/04/29/security-release-gitlab-11-dot-10-dot-2-released/