Trusted vs untrusted ssh/X connections

[Larry Hall (Cygwin)]

On 06/19/2014 04:25 PM, Andrew DeFaria wrote:
> This is something that's been bothering me for a long time and I thought I
> might look into it a little deeper. I'm not sure if I should post this here
> because it involves Cygwin/X but it also involves OpenSSh.

Actually, this is probably off-topic since I don't see anything Cygwin-
specific about setting up ssh/X connections.

> When I ssh into a Linux machine using ForwardX11 I get those familiar messages:
>
> Warning: untrusted X11 forwarding setup failed: xauth key data not generated
>
> and according to https://cygwin.com/ml/cygwin-xfree/2008-11/msg00154.html:
> The warning can be silenced by using ssh -Y, since that
> is what ssh -X is doing now anyway.
>
> However, I find -Y to be 20 times slower to log in than -X:

This is probably a configuraton issue since when I ssh into my Linux system,
login time is roughly equivalent.

> Adefaria-lt:time ssh cm-job-ldev01 echo 'hi'
> Warning: untrusted X11 forwarding setup failed: xauth key data not generated
> Warning: No xauth data; using fake authentication data for X11 forwarding.
> /usr/bin/xauth:  error in locking authority file /home/adefaria/.Xauthority
> hi
>
> real    0m2.387s
> user    0m0.075s
> sys     0m0.446s
> Adefaria-lt:time ssh -Y cm-job-ldev01 echo 'hi'
> Warning: No xauth data; using fake authentication data for X11 forwarding.
> hi
> /usr/bin/xauth:  error in locking authority file /home/adefaria/.Xauthority
>
> real    0m22.476s
> user    0m0.091s
> sys     0m0.477s
> Adefaria-lt:
>
> Bonus points if you can help me get right of the other errors!

I believe the error regarding the .Xauthority file has something to do with
the permissions on the file.  As for the warning, I believe you want to
unset DISPLAY on your PC, set X11Forwarding to "yes" on your Linux machine
in your sshd_config file, and X11Forward to "yes" in you ssh_config file
(for instance) on your PC.  At least, that's what I gathered from searching
around on the net for the information. :-)

I think it goes without saying that enabling X11Forwarding opens up
some security holes in X.  Oops, looks like I said it anyway. ;-)


-- 
Larry

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