Kibana versions after 5.1.1 and before 5.6.7 and 6.1.3 had a cross-site scripting (XSS) vulnerability in the tag cloud visualization that could allow an attacker to obtain sensitive information from or perform destructive actions on behalf of other Kibana users.
https://discuss.elastic.co/t/elastic-stack-6-1-3-and-5-6-7-security-update/117683