Possible Remote Code Execution in /System/MediaEncoder/Path via UNC paths (GHSL-2023-029)

The /System/MediaEncoder/Path endpoint executes an arbitrary file using ProcessStartInfo via the ValidateVersion function. A malicious administrator can setup a network share and supply a UNC path to /System/MediaEncoder/Path which points to an executable on the network share, causing Jellyfin server to run the executable in the local context.

public bool ValidateVersion()
        {
            string output;
            try
            {
                output = GetProcessOutput(_encoderPath, "-version", false, null);
            }

This has been a potential endstep of several other attack vectors, and as such, this endpoint is being removed.

This issue was discovered and reported by GHSL team member @Kwstubbs (Kevin Stubbings).