full-disclosure - Re: noise about full-width encoding bypass?

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Message-ID: <62134.131.182.176.99.1179776518.squirrel@slashmail.org>
Date: Mon, 21 May 2007 14:41:58 -0500 (EST)
From: "Steven Adair" <steven@...urityzone.org>
To: "Brian Eaton" <eaton.lists@...il.com>
Cc: Full-Disclosure <full-disclosure@...ts.grok.org.uk>,
	Web Security <websecurity@...appsec.org>
Subject: Re: noise about full-width encoding bypass?

> On 5/21/07, ascii <ascii@...amail.com> wrote:
>> Brian Eaton wrote:
>> > To summarize what I've heard from various sources: I am missing
>> > something important. =)  Both PHP and ASP.NET will decode these
>> > characters into their ASCII equivalents.
>>
>> (AFAIK)
>>
>> Only ASP.NET/IIS decodes that automatically.
>>
>> PHP *can* do that as like JSP and probably others but that has
>> to happen explicitly in the application code or on an other layer.
>
> (Cracking up that somebody going by the handle ascii is commenting on
> character encoding issues. =)
>
> Given how few application platforms decode full-width unicode to ASCII
> equivalents, is there a case to be made that those application
> platforms that do decide this conversion is a good idea are broken?
>
> Put another way: should this be considered a bug in ASP.NET?
>

I think you could be on either side, but I would learn towards this being
a feature than a bug.  Multiple products appear to do the decoding in the
same manner and intentionally perform this function.  However, the recent
advisories that went out were geared towards IDS/IPS products that were
not designed to be able to recognize such half-/full-width encoded
traffic.  Unless there is some RFC or generally followed documentation
saying the traffic should not be encoded/decoded as such, I would continue
to lean towards this being a feature.  It just appears to be a place much
of the IT (security) world has overlooked.

Steven
securityzone.org

> Regards,
> Brian
>
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