RE: How to handle "special characters"

["Keifer, Trey" <Trey.Keifer () fishnetsecurity com>]

If you *have* to deal with special characters you will want to encapsulate everything at each level
depending on what you need to deal with and then peel off that encapsulation at each sub-level within
your application while keeping the idea of least-acceptance in mind. This has the added benefit of
ensuring input checking at every level in your application which, from my experience, seems to be the
root of most problems. People implement one layer of protection and either the malicious user finds a
way around it or they forget to do it *everywhere* so the one place they missed puts them on CNN. 

In a perfect world, every function would verify both the data its given and the data it returns and
XSS would become a non-issue.

Trey Keifer
Security Engineer - Level II
Fishnet Security

Office: 816.421.6611
Cell: 816.710.6830
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http://www.fishnetsecurity.com


-----Original Message-----
From: Sekurity Wizard [mailto:s.wizard () boundariez com]
Sent: Wednesday, December 10, 2003 7:34 AM
To: webappsec () securityfocus com
Subject: How to handle "special characters"


Greetings,
  I had a developer pose an interesting question today, and I wasn't 100% sure what the answer was -
so I figured I'd turn to the community for advice.

  There are certain characters which pose threats at different levels of the application tier model.
Some at the client, some at the web server, and others in the database.  Characters such as the &, |,
', ", and - can be associated with database hacks, for the most part.  If a requirement is there to
absolutely keep these characters in, for example, interface with a back-end legacy database, whats the
best way to handle their existance?  As a developer, what are the necessary and proper steps to take
to avoid SQL Injection, command execution or other attacks?

Just looking for some good best-practices..
  s.Wizard

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