Navidrome has authentication bypass in Subsonic API with non-existent username

Navidrome is an open source web-based music collection server and streamer. Starting in version 0.52.0 and prior to version 0.54.5, in certain Subsonic API endpoints, a flaw in the authentication check process allows an attacker to specify any arbitrary username that does not exist on the system, along with a salted hash of an empty password. Under these conditions, Navidrome treats the request as authenticated, granting access to various Subsonic endpoints without requiring valid credentials. An attacker can use any non-existent username to bypass the authentication system and gain access to various read-only data in Navidrome, such as user playlists. However, any attempt to modify data fails with a "permission denied" error due to insufficient permissions, limiting the impact to unauthorized viewing of information. Version 0.54.5 contains a patch for this issue.