bugtraq - Re: PHP security (or the lack thereof)

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Date: Fri, 23 Jun 2006 13:16:03 -0700
From: Crispin Cowan <crispin@...ell.com>
To: nabiy@...mail.com
Cc: bugtraq@...urityfocus.com
Subject: Re: PHP security (or the lack thereof)

nabiy@...mail.com wrote:
> Trying to make the language 'safe' won't fix it because the language is not the problem. The real problem is the way PHP is presented to most new developers.
>
>
> PHP has been introduced as a tool for the web developer. As a language its goal is "to allow web developers to write dynamically generated pages quickly." (  http://www.php.net/manual/en/faq.general.php ). The focus then is to enable the web developer by giving him the tools he needs to create dynamic content, with as little hassle as possible. The web developer need only read a short tutorial ( http://www.php.net/manual/en/tutorial.php ) and he is ready to read, understand and implement the ideas presented in the various example scripts on PHP.net. Unfortunately this situation leaves the web developer uninformed and unprepared to face the hostile environment that is the net.
>   
That is a fascinating perspective.

Web developers who work with static content (HTML and images, etc.) is
pretty secure: the security threat amounts to Apache configuration
(directory browsing and htpasswd stuff) and it is pretty difficult for
an attacker to corrupt static content by way of the content.

Dynamic content, while not inherently dangerous, becomes dangerous when
you hand the web developer a Turing-complete language. Suddenly the
exact behavior of the web site under arbitrary input becomes
undecidable. Programmers (mostly) know this. Security developers
(should) know this. Web artists may have just been introduced to
programming to get their web site to be dynamic.

There are two possible approaches to fixing this. One, as nabiy
suggests, is to change how PHP is presented to web developers. Label it
as a chain saw, and point out that chain saws don't know the difference
between "log" and "leg" :)

The other is to contrive a language that is both sufficient for dynamic
web content development, and also *not* Turing-complete. I have no idea
what such a language might look like, or even whether the intersection
of these two requirements is the null set.

For more on Turing completeness and security, consider coming to USENIX
Security 2006 and see my talk on this topic "Turing Around the Security
Problem" http://www.usenix.org/events/sec06/tech/#thurs

Crispin

-- 
Crispin Cowan, Ph.D.                      http://crispincowan.com/~crispin/
Director of Software Engineering, Novell  http://novell.com