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.
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.