The fix in Kibana for ESA-2017-23 was incomplete. With X-Pack security enabled, Kibana versions before 6.1.3 and 5.6.7 have an open redirect vulnerability on the login page that would enable an attacker to craft a link that redirects to an arbitrary website.
https://discuss.elastic.co/t/elastic-stack-6-1-3-and-5-6-7-security-update/117683