openssh unix dev - Jun 2001 - Disabling Password-based auth? (was RE: recent breakins)

All--

But it's not as simple as forwarding the password-based
authentication.  Regardless of what method was used to
SSH from system one (user's) to system two (SF), the
user then started up *a second* SSH session to go
from two (SF) to three (Apache).  There is no effective
way for any authentication information from the first
session to be passed to the second, in my mind.

Remember that the SF servers had suffered a root
compromise--so any non-password-based authentication
that would allow the user on the SF system to get to
the Apache systems could have been equally compromised.

The correct fix is *not* to disable password-based
authentication, but to ensure that users understand
that SSH is not a silver bullet.  An SSH session should
generally only be initiated from a more secure system
to a less secure system--in my case, the system on my
desk is one that I have personally hardened and that
is closely monitored, so I have no problem using SSH
to go out to my ISP and read mail.  I would think
*very* carefully before using SSH in reverse, since my
ISP's systems are (IMHO) much less secure.

I'm as appalled by what happened to SF and Apache as
anyone else, but I would ask that we work on the
user awareness issue, which I believe is the real
"root" problem (pardon the pun).  For the cases
where someone needs to get from system A to system B
with some basic level of security and doesn't have any
other credentials/authentication available, there really
is no substitute for password-based authentication.

--
Rip Loomis
Brainbench MVP for Internet Security
http://www.brainbench.com (Transcript 1923411)

> -----Original Message-----
> From: Tom Holroyd [mailto:tomh at po.crl.go.jp]
> Sent: Friday, June 01, 2001 4:53 AM
> To: openssh-unix-dev at mindrot.org
> Subject: Re: recent breakins
> 
> 
> On Fri, 1 Jun 2001, Gert Doering wrote:
> 
> > On Fri, Jun 01, 2001 at 11:24:49AM +0900, Tom Holroyd wrote:
> > > But what about multiple links?  It should be possible to forward
> > > authentication requests back to the user's keyboard.  The 
> SRP protocol can
> > > be forwarded over any number of links, *even through a 
> trojaned ssh*
> > > without revealing any information that a cracker can use.
> >
> > Same with agent forwarding and using RSAAuthentication.
> 
> True.  Too bad the guy wasn't using it.  Why wasn't he using it?
> 
> Perhaps OpenSSH should simply disallow password authentication?
> 
> This type of man-in-the-middle attack (trojaned ssh) is not 
> theoretical
> anymore, and password authentication is broken.
> 
> 
> The question is, can password authentication be (securely) 
> forwarded?  If
> not, then we really should remove password authentication as 
> an option.
>

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

> But it's not as simple as forwarding the password-based
> authentication.  Regardless of what method was used to SSH from system
> one (user's) to system two (SF), the user then started up *a second*
> SSH session to go from two (SF) to three (Apache).  There is no
> effective way for any authentication information from the first
> session to be passed to the second, in my mind.
> 
> Remember that the SF servers had suffered a root compromise--so any
> non-password-based authentication that would allow the user on the SF
> system to get to the Apache systems could have been equally
> compromised.
That's exactly the point of SRP (well, one of the points) - it takes care
of that - even if the host in the middle has been compromised and the
attacker is sniffing all the ttys or something

One can imagine other ways of ssh'ing through multiple systems without
giving away passwords to the intermediate hosts.  A trivial example -
instead of saying "ssh -t host1 ssh host2" we can say instead
"ssh -f -L 2222:host2:22 host1 'sleep 999999'; ssh -p 2222
localhost" -
the latter commandline never allows host1 to see the plaintext of your
password/key/whatever for host2.


 -Jason

 ---------------------------
 If the Revolution comes to grief, it will be because you and those you
 lead have become alarmed at your own brutality.         --John Gardner



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (FreeBSD)
Comment: See https://private.idealab.com/public/jason/jason.gpg

iD8DBQE7F5+1swXMWWtptckRAkBZAKCsXTzgmEebtaXiLaDiGfJwQVaqbACgpN2N
zPTJ9c7I+aKTnR/RnFUqw0w=TlgR
-----END PGP SIGNATURE-----