A flaw was found in Grafana 2.x, 3.x, and 4.x before 4.6.4 and 5.x before 5.2.3 allows authentication bypass because an attacker can generate a valid "remember me" cookie knowing only a username of an LDAP or OAuth user.

References: https://grafana.com/blog/2018/08/29/grafana-5.2.3-and-4.6.4-released-with-important-security-fix/

In Grafana 2.x through 6.x before 6.3.4, parts of the HTTP API allow unauthenticated use. This makes it possible to run a denial of service attack against the server running Grafana.