RE: Write-up by Amit Klein: "Forging HTTP request headers with Flash"

["James Pujals" <james.pujals () sterlingpayment com>]

> >
It's trivial for the attacker to forge any HTTP request header when the attacker is in
DIRECT contact with the web server. And I think that's what you refer to, as well as the
OWASP text you quoted.

But the picture was considered to be significantly different when the attacker was NOT in
direct contact with the server. That is, the attacker is able to serve malicious HTML
content to the victim, who uses a browser. In such scenario, the attacker is limited to
whatever the victim's browser can do across domains. And that's very limited (well, unless
you throw in Flash...). Sure, you can send requests to URLs with any parameters (and that's
quite interesting in itself, see today's message -
http://www.webappsec.org/lists/websecurity/archive/2006-07/msg00086.html), but until this
week, there was no control over the HTTP request headers that are sent across domain (well,
you could inject data into some parts of the Referer header - not the entire host though,
and you could control part of the host header, but not much beyond that). This browser
limitation is what I meant when I wrote "implicit assumption".

I hope that clarifies my statements.
<<
 
Thanks for your response and clarification.  Perhaps I'm missing something, but I do not see how this particular 
vehicle of attack changes the original known threat.  Are you implying that the user (whose browser renders the 
malicious flash unknowingly) is open to new risks by this mechanism?  As I understood your original report, the threat 
was on the web application itself (and thus your comment about how they shouldn't rely on the inviolability of the HTTP 
headers), and if so, it is just the same threat as I mentioned before.
 
I'm not trying to challenge your argument, I'm just trying to understand it better, as I may be understanding it.
 
In any case, your findings are certainly interesting, and something that should be addressed not only by browser 
implementors, but by Adobe on its Flash framework (and of course, by web developers, but I take that as a given).
 
     -dZ.

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