proftpd chroot option

Hello everyone,
While reading proftpd's documentation, I came across something regarding their DefaultRoot option, which makes a chroot call to put them in a chroot jail at login:

Quote:

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When the specified chroot directory is a symlink this will be resolved to it's parent first before setting up the chroot. This can have unwanted side effects. For example if a chroot is to be configured within space to which a user as shell access, the chroot directory could be converted to a symlink pointing at '/'. Thus the chroot would be to the root directory of the server.
(Originally from http://proftpd.linux.co.uk/docs/dire...faultRoot.html)

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I'm still in the process of setting up webhosting. This says if they have shell access, they're able to make a symlink, and possibly exploit the issue. I wasn't planning on giving them shell access at all, but possibly restricted CGI access (via sbox, a cgi wrapper, which also chroots the script to their home directory, and I might add that I set that up successfully :) )

So, would that security hole be an issue even if I only give them a 'jailed' home directory and 'jailed' cgi script access?

Thanks
-Mike

If you make the chroot a directory in a directory they don't have write access to, it's not a problem.

Then it still wouldn't be a problem unless they can make a CGI script that modifies it, which it probably wouldn't be able to right, because the CGI runs as a different user?

Typically, chrooting them to their home directory is very safe.

Oh yes, and this thread probably should have been in "*nix security" instead of chit-chat. It also gets on the front page so you will get a much better response.

Thanks for your reply, slarty.

Is there anything else I should know before starting a webhosting thing (like security settings I should change, things I should be aware of, etc)?

I might also enable SSI (IncludesNOEXEC) and limited .htaccess abilities for the users. Would that be a problem at all?

Also, to the admins/moderator, if you could please move this thread to the *nix security discussion forum. Sorry about the mishap.

Thanks