From: ken at vanwyk.org (Kenneth R. van Wyk)
Subject: Re: Gates: 'You don't need perfect code' for good security

Jeremiah Cornelius posted an excerpt from an interview with Bill Gates earlier 
here.  FYI, in response to Mr. Gates's quote, my co-author and I have written 
an _opinion_ piece, included below.  We feel pretty strongly that Mr. Gates 
is missing (at least) a couple of important issues.

Cheers,

Ken van Wyk

=====

31 October 2003

In a recent interview for ITBusiness.ca (full text available at
http://www.itbusiness.ca/index.asp?theaction=61&sid=53897), Microsoft
Chairman and Chief Software Architect Bill Gates is quoted as having
said:

      You don't need perfect code to avoid security problems. There
      are things we're doing that are making code closer to perfect,
      in terms of tools and security audits and things like that. But
      there are two other techniques: one is called firewalling and
      the other is called keeping the software up to date. None of
      these problems (viruses and worms) happened to people who did
      either one of those things. If you had your firewall set up the
      right way -- and when I say firewall I include scanning e-mail
      and scanning file transfer -- you wouldn't have had a
      problem.

Mr. Gates overlooks here two critical points.

First, firewalling and patching can not in fact shield networks from
all of the impact of worms and viruses. Ask any experienced network
admin. There will always be users who bring into a firewalled network
a laptop that was, for example, infected at home. Once that infected
laptop is connected to the enterprise, the firewall is irrelevant.
Worse yet, no matter how aggressively a company has propagated a patch
throughout the network, the routine influx of vulnerable, unpatched
systems (from that same migrant laptop community) will continue to
supply fresh meat for the malicious software.

Second, the security of the application itself is tightly bound to
its design and implementation as well. A company that writes its own
business software could well go broke following Mr. Gates's advice.

To illustrate this, let's consider a hypothetical example that is very
realistic in today's business environment.  A company writes a
web-based application that enables its customers to login and purchase
its goods.  In keeping with Mr. Gates's recommendations, they install
a high quality, state of the art firewall and put in place processes
for rapidly installing every security patch that Microsoft releases.
(Perhaps they test them in a controlled lab environment first.)

Now, let's further say that the team that wrote the application
software took the above quote by Mr. Gates to be accurate.  But it
turns out that there's a problem in the software that the team wrote.
Because their front-end software (that runs on their web server)
doesn't properly screen users' input -- after all, "you don't need
perfect code" -- and an attacker discovers that a vulnerability known
as "SQL Insertion" exists in the application.  The SQL Insertion
vulnerability enables the attacker to enter SQL-based database
inquiries directly to the back-end database server, and make
read/write changes to the database at will -- perhaps he would change
the price of his purchase to $0 and the quantity of his order to
1000, or some such.  You get the drift.

In this hypothetical example, the firewall did its job perfectly.
All systems had up-to-date security patches installed. Yet the
attack succeeded at compromising the database system (AKA the
company's crown jewels).

While it's true that "perfect code" is probably not achievable,
you do need "secure enough" code; and achieving that takes a great
deal more than a good firewall and patch maintenance processes.  It
takes a sound design, built on top of a firm architecture. It takes
an implementation of the software that is free of such common flaws as
SQL Insertion, buffer overflows, and the like. And, it takes a well
designed and operated production environment with a firewall and such.

Every Software Designer and Software Architect in major corporations
needs to understand these principles if their own network and business
applications are to be secure.

Mark G. Graff
Kenneth R. van Wyk
Authors, Secure Coding
http://www.securecoding.org

Copyright (C) 2003, Mark G. Graff and Kenneth R. van Wyk.
Permission granted to reproduce and distribute in entirety with credit to 
authors.

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