Hi Achim -
On 4/30/06, Achim Hoffmann <kirke11@securenet.de> wrote:
In contary hidden fields can only be attacked within the application itself,
more specific in the page they are used. Session riding is impossible, session
fixation very hard, just session hijacking remains but is not simple too (I'm
talking about automated attacks, not shoulder surfing).
I think this is where one of us is confused. =)
Amit's note on "Path Insecurity" described how to execute javascript
in the context of another document on the same server. Is "Path
Insecurity" somehow limited to XSS attacks on cookies? I don't
believe so; I suspect the same techniques AK used in that paper to
steal cookies that were accessible to other documents apply equally
well to reading hidden form fields in those documents.
I may be missing something from Amit's paper, though. Please fill me
in if I am wrong.
Assuming I did understand Amit's paper properly, nearly all of the
attack techniques you listed in your note apply equally to hidden form
fields and cookies. There are some practical differences. For
example:
- Session fixation is easier with form fields than with cookies. If
form fields are used for sessions, a session fixation attack can be
performed from any web server. If cookies are used, it can only be
done from another web server in the same DNS domain. Assuming the
application developer does the right thing and changes the session
cookie after authentication, session fixation is not possible in
either case.
- It is easier to steal a domain cookie than to steal a hidden form
field. To steal a domain cookie, you just need a vulnerable server in
the same domain. Stealing a form field requires a vulnerable page on
the server hosting the form.
The one distinct advantage cookies have over form fields is IE's
HttpOnly cookie extension. HttpOnly doesn't make attacks impossible,
but it certainly does raise the bar a bit.
Regards,
Brian
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