Grafana users with email as a username can block other users from signing in

Vulnerability Description

Grafana is an open source data visualization platform for metrics, logs, and traces. Versions prior to 9.1.8 and 8.5.14 allow one user to block another user's login attempt by registering someone else'e email address as a username. A Grafana user’s username and email address are unique fields, that means no other user can have the same username or email address as another user. A user can have an email address as a username. However, the login system allows users to log in with either username or email address. Since Grafana allows a user to log in with either their username or email address, this creates an usual behavior where `user_1` can register with one email address and `user_2` can register their username as `user_1`’s email address. This prevents `user_1` logging into the application since `user_1`'s password won’t match with `user_2`'s email address. Versions 9.1.8 and 8.5.14 contain a patch. There are no workarounds for this issue.

References

• https://github.com/grafana/grafana/releases/tag/v9.1.8
• https://github.com/grafana/grafana/security/advisories/GHSA-gj7m-853r-289r
• https://github.com/grafana/grafana/commit/5644758f0c5ae9955a4e5480d71f9bef57fdce35