The avatar feature in Grafana 3.0.1 through 7.0.1 has an SSRF Incorrect Access Control issue. This vulnerability allows any unauthenticated user/client to make Grafana send HTTP requests to any URL and return its result to the user/client. This can be used to gain information about the network that Grafana is running on. Furthermore, passing invalid URL objects could be used for DOS'ing Grafana via SegFault. It's also possible to escalate this vulnerability to RCE.
Upgrade to the lastest version of Grafana. This issue was fixed in Grafana 6.7.4 and 7.0.2.
If for some reason you cannot upgrade, the impact can be mitigated by blocking access to the avatar feature by blocking the /avatar/* URL via a web application firewall, load balancer, reverse proxy, or similar. It can also be mitigated by restricting access to Grafana.