Mailinglist Archive: opensuse-security (465 mails)

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RE: [suse-security] sftp without without a valid shell?
  • From: John Ritchie <ritchiej@xxxxxxxxxxxxxxxxxxxxxxxxx>
  • Date: Sat, 1 Dec 2001 11:19:57 -0800 (PST)
  • Message-id: <Pine.LNX.4.33.0112011104420.21010-100000@xxxxxxxxxxxxxxxxxxxxxxxxx>

OK, I'm _Really_ behind in my suse-security reading. I hope everybody
hasn't already moved past this onto better things.

On Tue, 6 Nov 2001, Boris Lorenz wrote:

> Hi,
>
> On 06-Nov-01 Thorsten Marquardt wrote:
> > Hi List,
> >
> > I like to offer some customers a kind off sftp account but to deny any login
> > to this accounts. So I thought about having /bin/false as shell in
> > /etc/passwd
> > but this prevents sftp to. What can I do?
>
> www.ssh.com offer a shell called ssh-dummy-shell, which provides any hooks for
> secure file transfer via sftp, but denies access to a real shell. Just replace
> the std shell entry in your /etc/passwd with it.
>
> Other shells (e. g. /bin/false) won't work because sftp actually uses a normal
> ssh tunnel to transmit data, so it needs a more special treatment like std ftp.
>
> This ssh-dummy-shell is part of the SSH server package, and also of the Windows
> Client-Pack (which also includes all server components).
>
> However, the Win-Client-Pack isn't free.
>
>
> > Thanks in advance
> >
> > Thom
>
> Boris Lorenz <bolo@xxxxxxx>
> ---


I tried the ssh-dummy-shell from ssh.com but it didn't interoperate with
openssh although it worked perfectly on some of our systems that were
running ssh.com's SSH server. I didn't try a PAM approach.


The way I solved this (on Solaris with Openssh) was to set the sftp-only
user's shell to be the sftp-server binary (/usr/local/libexec/sftp-server
on my Solaris openssh build). I did not have to add this to /etc/shells.
I haven't tried this on a SuSE box.

The above solution has been working for several months without a hitch.
My sftp-only users are connecting with ssh.com's commercial winblows ssh
client, v. 3.0.x but I tested it with v 2.4 and also with linux and
solaris openssh clients.

If I missed some security implication in the above approach let me know.
:)

John Ritchie


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