qemu.conf claims:

# The default VNC password. Only 8 letters are significant for
# VNC passwords. This parameter is only used if the per-domain
# XML config does not already provide a password. To allow
# access without passwords, leave this commented out.

# An empty
# string will still enable passwords, but be rejected by QEMU,
# effectively preventing any use of VNC.
=> This seems to be wrong, and empty string "" leads to an empty password being accepted.

For spice_password it works however as described.


# Obviously change this
# example here before you set this.


As long as VNC/SPICE cannot be used via UNIX sockets, you should really allow disabling either of both completely for security reasons.


Cheers,
Chris.