Kibana contains an embedded version of the Chromium browser that the Reporting feature uses to generate the downloadable reports. If a user with permissions to generate reports is able to render arbitrary HTML with this browser, they may be able to leverage known Chromium vulnerabilities to conduct further attacks. Kibana contains a number of protections to prevent this browser from rendering arbitrary content.
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):