Some Interesting Topics arising from the SANS/CWE Top 25

[jim at manico.net (Jim Manico)]

> I'd like to offer a different view for your consideration, which is
that /*input validation and output encoding actually don't have anything
to do with security*/. Those techniques are essential software building.

I'm really confused with this statement - and almost feel it's
dangerous. Encoding, especially, is the cornerstone of building secure
web applications. In particular, _encoding data within the correct
context of usage_  is the basis for defending against approximately 2/3
of all classes of web vulnerabilities - XSS and SQLi in particular.
Sure, bad or no encoding is definitely a bug - but it's also impossible
to build a "secure" web application without proper use of encoding. So
to say that "output encoding actually don't have anything to do with
security" seems like a fairly radically incorrect statement. Sure, we
should split up encoding into multiple categories - but I still think
it's the cornerstone to secure programming practices. Libraries like
ESAPI make such tasks very easy, too.

However, I agree that Validation is overhyped. Input validation is
really relevant to (web) security if you ever accept HTML from a user
(ala validation tools like AntiSamy). You also need to solve malicious
file upload attacks (if you support that feature) with input validation.
Of course there are different considerations for the think client world
when it comes to this topic.

So, in short:

Encoding and Validation are software building blocks -> that are
fundamental for (especially web) software to defend against injection
attacks (at least) -> therefore making validation and coding have
something to do with security

- Jim


> blocks. While it is true that omission to use these techniques often
> causes security issues, that only means such programs are insecure in
> addition to being defective. I think that it's inherently wrong to
> associate input validation and output encoding with security. Fix the
> defects and the security issues will go away. On the other hand, if
> you only fix the security issues you may be left with a number of
> defects on your hands.
>
> Input validation layers should focus on accepting only valid data (per
> business requirements), while code that transmits data across system
> boundaries should focus on using the exchange and communication
> protocols correctly.
>
> Actually, now that I think about it more, I think we are struggling
> with the term input validation because the term has been overloaded.
> In the one sense, we are talking about validating user input, which
> mostly needs to concern itself with adhering to business requirements.
> This meaning is not very important for security, but the other one,
> validating data before something is done with it, is. If you take a
> web application for example, you would ideally verify that all user
> submitted data adheres to your business requirements.
>
>   

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