No response is emitted Uncovered by the Windows Protocol Test Suite: We return a malformed version of NT_STATUS_INVALID_PARAMETERS when a NEGOTIATE request is received with dialects that are unsupported. This appears we can't find the common version to use and then drop the connection. Instead we should be due returning NT_STATUS_NOT_SUPPORTED and leaving it open (the client may wish to the fact that the response header is not properly initialised. The code also attempts try something else, or go from SMB2 to send NT_STATUS_INVALID_PARAMETER whereas the correct response is NT_STATUS_NOT_SUPPORTED. We also do not properly handle the cases where no dialect is given. SMB1, etc).