In Redmine before 3.2.8, 3.3.x before 3.3.5, and 3.4.x before 3.4.3, XSS exists in app/helpers/application_helper.rb via a multi-value field with a crafted value that is mishandled during rendering of issue history.
https://www.redmine.org/projects/redmine/wiki/Security_Advisories
https://www.redmine.org/issues/27186
https://www.debian.org/security/2018/dsa-4191
https://github.com/redmine/redmine/commit/94f7cfbf990028348b9262578acbc53a94fce448