Quoting Arnt Karlsen (a...@iaksess.no):

> ..my prefecence was the -X option: ssh -X root@localhost
> until Debian killed it with some new policy.

Was it Debian that did that?  I was never sure.  I just remember that
'ssh -X' suddenly no longer did X11 forwarding as it used to, but I
looked up the problem and saw that 'ssh -Y' now did that.  I never
chased down the matter further.

(/me Web-searches:)

It has something to do with 'untrusted X11', mentioned in passing here:
https://unix.stackexchange.com/questions/12755/how-to-forward-x-over-ssh-to-run-graphics-applications-remotely

-Y 'enables trusted X11 forwarding':

https://serverfault.com/questions/273847/what-does-warning-untrusted-x11-forwarding-setup-failed-xauth-key-data-not-ge

  "Untrusted" in this context means you don't trust the connection. SSH
  will use additional security measures to try to make X11 forwarding
  safer. "Trusted" means you are entirely confident that no on on the
  remote host will get access to your Xauth data and use it to monitor
  your keystrokes for instance.

  This terminology actually confused me for years. I thought "Trusted"
  connections were safer. But actually it's an option you're supposed to
  use in situations where the connection IS trustworthy and you want to
  run stuff without extra security measures getting in your way.
  "Untrusted" is the one that makes it (somewhat) safer to deal with an
  untrusted remote host.

  An "Untrusted" connection attempts to limit what a black hat could do to
  you by engaging the X11 security extension and disabling other
  extensions that you (hopefully) don't need. This is probably why RandR
  is disabled with -X. Do you need to be able to rotate your X display
  from the remote host?

  It's also important to note that "untrusted" X11 forwarding turns off
  after a certain amount of time to keep you from accidentally leaving it
  on. New attempts to open windows will just fail after that. That bit me
  several times before I read enough docs to understand what was
  happening.

My surmise is, not a Debian change, so much as a Portable OpenSSH change.

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