ssh -t <host> /bin/sh trick (was Re: ftp access)

From: Paul Herman (pherman@frenchfries.net)
Date: 02/28/01 

Date: Wed, 28 Feb 2001 09:09:49 +0100 (CET)
From: Paul Herman <pherman@frenchfries.net>
To: Steve Reid <sreid@sea-to-sky.net>

On Tue, 27 Feb 2001, Steve Reid wrote:

> On Tue, Feb 27, 2001 at 02:55:12PM -0800, Brooks Davis wrote:
> > If you do this be sure to keep users from being able to access the system
> > via ssh. Otherwise they can just use ssh to spawn a shell for themselves:
> > ssh -t <host> /bin/sh
>
> Are you certain about this?
>
> I tried this on a 4.1.1-R box I operate and it didn't let me in. The
> box is set up with the ftp login shell set to "/nonexistent/ftponly",
> which is listed in /etc/shells but does not exist.

This behaviour has changed over the years, which is why there are two
conflicting reports.

I remember the days (FreeBSD 2.2.6, or so, using ssh from ssh.com) of
having to write a small script in /etc/sshrc which checks for invalid
shells to prevent what Brooks was describing. Back then, it *did*
work.

Now (at least with OpenSSH_2_3_0), that trick doesn't work anymore.
Don't know when/where/in which version this changed, but my inkling is
that PAM is the culprit.

-Paul.

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