Kibana versions 5.3.0 to 6.4.1 had a cross-site scripting (XSS) vulnerability via the source field formatter that could allow an attacker to obtain sensitive information from or perform destructive actions on behalf of other Kibana users.
https://www.elastic.co/community/security
https://discuss.elastic.co/t/elastic-stack-6-4-1-and-5-6-12-security-update/149035