Finally managed to create a jailed SFTP server, but how secure?

Larry Hall (Cygwin)
Tue Dec 2 17:02:00 GMT 2008

TheO wrote:
>> If you're happy with the results, that's fine.  However, you asked how
>> secure SFTP was.  The answer is as I've said.  Cygwin is not the O/S.
>> It cannot enforce restrictions on the O/S.  Only the O/S can restrict
>> or grant access to users.
> Thanks Larry,
> The reason why Cygwin is ideal for me to provide SFTP service is that it
> provides a free SFTP solution for Windows platform. My programmers come
> from Windows world, they are more familiar with .NET than Unix but sometimes,
> they are required to build a system featuring an SFTP server where our user
> can upload his files to be processed by our .NET application and finally,
> he download the response files from SFTP. Cygwin makes this possible in an
> economic way.

I understand.  If SFTP under Cygwin fits your needs and you can live
with the risks, then you should continue using it.  I certainly don't
understand your application or its requirements for communication but
given your description above, it seems to me that 'scp' would serve your
purpose and wouldn't rely on a limited 'chroot' capabilities.  But I'm
assuming you've already thought of that and have ruled it out for your
own reasons.

>> I have not attempted to set up a jailed SFTP environment on Cygwin.  It
>> may be that what you've done hems the user into the area you want when
>> he/she is using Cygwin tools.  However, this does not restrict the user
>> with Windows native tools.  If he/she is able to leverage those inside
>> the jail, then the user has the keys he/she wants to get out.
> He might be able to upload "nasty" tools but What else could he possibly do 
> if he has access to only a restricted SFTP subsystem? 

Good question.  A better one is are you willing to accept the risk?  I also
want to once again point out that "a restricted FTP subsystem" does not
have all the same restrictions as it would in a UNIX/Linux environment.
Only you can decide whether this difference is something you can live
with.  But in terms of security, Cygwin's SFTP is not as secure as
UNIX/Linux versions with the full O/S support for 'chroot'.  I'm not
trying to talk you out of anything.  I'm just answering your original
question and providing you with the facts.  It's up to you how you want
to apply them to your situation.

Larry Hall                    
RFK Partners, Inc.                      (508) 893-9779 - RFK Office
216 Dalton Rd.                          (508) 893-9889 - FAX
Holliston, MA 01746


A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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