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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