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RE: Adding "X11UseLocalhost no" to /etc/ssh/sshd_config breaks x forward

from [Lewis E. Randerson] Network Security [Permanent Link]
Subject: RE: Adding "X11UseLocalhost no" to /etc/ssh/sshd_config breaks x forwarding
Date: Tue, 3 Apr 2007 07:36:22 -0400 
Darren,

Those tests have been made and have come up negative. 


Does "thathost.pppl.gov" resolve to the correct IP address?

   
  Yes.  Thishost was only a name for e-mail purposes.  It's
  real name and the reverse lookup resolve correctly.


Are there any iptables rules that would apply to that connection?


  No.  This problem also occurs when iptables are turned off.


If you try to connect to the port with telnet (ie "telnet

  thathost.pppl.gov 6013" in this example) what error does it give?

  (This time 6011 is the relevant port number)

  telnet <hostname> 6011
  Trying <ipaddress>...
  telnet: connect to address <ipaddress>: Connection refused
  telnet: Unable to connect to remote host: Connection refused

  Note: telnet <hostname> 22 works. 

So I am heading towards the thought: X forwarding with X11UseLocalhost
has been turned off either by Openssh or by Red Hat.  Whether a
feature or a bug I am unsure, there are warnings in the man page 
about this being a potential security issue.

--Lew 

-----Original Message-----
From: Darren Tucker [mailto:dtucker@zip.com.au] 
Sent: Monday, April 02, 2007 6:04 PM
To: Lewis E. Randerson
Cc: secureshell@securityfocus.com
Subject: Re: Adding "X11UseLocalhost no" to /etc/ssh/sshd_config breaks x
forwarding

Lewis E. Randerson wrote:

When using Red Hat built openssh-server-3.9p1-8.RHEL4.17.1,
X forwarding is breaking when "X11UseLocalhost no" is added
to configuration file /etc/ssh/sshd_config.  Following is an
example.

  thishost$ ssh -Y thathost.pppl.gov
  thathost$ xclock
  Error: Can't open display: thathost.pppl.gov:13.0

Command xauth -list does show the above display name. 


Does "thathost.pppl.gov" resolve to the correct IP address?  Are there
any iptables rules that would apply to that connection?  If you try to
connect to the port with telnet (ie "telnet thathost.pppl.gov 6013" in
this example) what error does it give?

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.
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