Re: CGI security on a shared web server

From: Steffen Dettmer (steffen@dett.de)
Date: 05/25/02 

Date: Sat, 25 May 2002 17:34:50 +0200
From: Steffen Dettmer <steffen@dett.de>
To: secprog@securityfocus.com

* Kurt Seifried wrote on Thu, May 23, 2002 at 14:05 -0600:
> One possible solution, assuming you need to write the data but not read it
> until later is to encrypt it, generate a public/private keypair using
> pgp/gnupg, load the public key onto the server with your app, have it write
> the files after encrypting the data. Thus you can retrieve the data (ftp,
> www, whatever) and then decrypt it at your leisure and use it.

I don't think that this makes things secure. If the web server
runs as nobody, the CGI script must be executable for nobody. The
secret key must be reable for nobody. Of course you can protect
it with a passphrase and use a non-reable (C/C++) CGI binary
"script" if avialable, but even then the passphrase can be
revealed by unauthorized persons, since the are able to run CGI
scripts with same user (nobody), and by thus they can execute
your binary with different libraries (trojaned libc or whatever)
and many other possible attacks. But of course it's not as
trivial as open a nobody-readable unprotected file.

To summarize, I don't think that you can build secure anythink in
a non-secure (or here: completely open) environment at all!

Maybe you should search an ISP that offers i.e. suexec'd CGI
scripting.

oki,

Steffen 

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