Re: New Santy-Worm attacks *all* PHP-skripts

[Paul Laudanski <zx () castlecops com>]

On Sat, 25 Dec 2004, Paul Laudanski wrote:

> [code]
> SecFilter "visualcoders\.net/spy\.gif\?\&cmd"
> SecFilter ":/"
> [/code]
>
> Just in case the URL changes, the latter should still get all sorts of:
>
> http://
> ftp://
>
> Naturally, the latter also filters on 
>
> %3a%2f

I've been noticing some filters out there that may be a little too all 
encompassing.  Just giving a heads up.

http://castlecops.com/article-5640-nested-0-0.html

[quote]
I've seen some folks filtering the echr or esystem from the GET requests. 
This is flawed, because they are often times preceded by 

%2525echr(x)

Where x is any character.

This turns into

%.chr(x)

Which is a concatenation in PHP, and the chr is a function call from php:

http://php.net/chr

So filtering on echr or esystem is not valid, as e is part of the 
hexadecimal code, and simply put, it can be replaced with another hex 
code, then the echr filter would not match.

Filtering then on chr doesn't work either, because you can multiple false 
positive matches:

chris
christmas
christ
etc 

Instead of focusing on the good characters, you need to focus on the bad 
characters like the tick mark.
[/quote]

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-- 
Regards,

Paul Laudanski - Computer Cops, LLC. CEO & Founder
CastleCops(SM) - http://castlecops.com
Promoting education and health in online security and privacy.


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