Dear all,

Some enterprising people scanned the whole range of IPv4 addresses for open
VNC servers [1] and my casual browsing seems to indicate that a lot of them
are QEMU VMs. I suspect that this is because just doing "-vnc :1" will
listen on/bind to "0.0.0.0" (ie. on all the interfaces).

My suggestion for improvement would be:
- change the behaviour of "-vnc :port" such that it listens on "127.0.0.1"
when the IP isn't specified
- if host is "0.0.0.0" (perhaps also include any routable IPv4 addresses -
and non-link-local IPv6 addresses) and no authentication method is
specified error out with a message like "It is recommended that you DO NOT
expose the VNC server directly to the public internet. If you are sure of
what you are doing, please specify an authentication method for the VNC
server. See the documentation for more details"

I'm happy to supply patches if people agree on the desired approach.

Happy Holidays!
Attila Balazs

[1] https://news.ycombinator.com/item?id=8810366

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