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Re: Write-up by Amit Klein: "Forging HTTP request headers with Flash"
From: 3CO <threecheeseopera () gmail com>
Date: Wed, 26 Jul 2006 22:43:01 -0400

FYI Flash9 added a new property for object and embed tags to prevent
this technique from being used: "allowNetworking":
http://livedocs.macromedia.com/flex/2/docs/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00001590.html

That page doesn't explicitly list LoadVars as being disallowed, but I
just tested, and it is true.

For instance, Myspace has added that to all embed tags to prevent fun
from occurring.

Great paper though (as usual); thanks.

On 7/26/06, Amit Klein (AKsecurity) <aksecurity () hotpop com> wrote:
Hi

A reader going by the nickname "xeek" pointed out to me that
the examples in the paper making use of the HTTP GET request
do not work as-is (thanks xeek!). After looking at the matter,
I realized that I made a silly mistake. In my research, I
toyed with the LoadVars.send() method with 2 arguments
(url and target window), and had Flash automatically
select the appropriate methd (GET if empty body, POST if
non-empty body). The exploit works fine this way. When I
documented my findings, I decided to explicitly add the HTTP
method, to clarify the write-up. BIG mistake - turns out
that in such case, Flash doesn't send the headers if GET is
used (sounds like a bug...). And pity I didn't verify the exact
code I used in the write-up...

Anyway, to summarize - there's a mistake in the document,
and it's easily fixed. In each GET example, simply remove
the explicit method (i.e. delete all instances of ,"GET" in
the write-up). For example (the first example in the paper):

[...]
req.send("http://www.vuln.site/some/page.cgi?p1=v1&p2=v2";,
         "_blank");

This works as advertised, and as also verified by xeek.

Thanks, and sorry for the mistake,
-Amit

















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