Hi Achim,
-----Original Message-----
From: Achim Hoffmann [mailto:kirke11@securenet.de]
Yes that's true.
But it's still more difficult to access a form field than a
cookie. Attacking form fields needs to know the DOM. The bar
is higher for form fields.
Unless I'm missing something, it should be a simple matter to enumerate
all form fields on a page with JavaScript and send all the data offsite.
I don't see why it would require knowledge of the DOM to accomplish
this. An attacker could just go through every form.elements array and
concatenate the values into a single request.
You're right here, but missing a part.
If the session ID is in the cookie, a session is created on
the server and the browser holds the session ID after the
session fixation attack and sends it automatically for (all)
following requests.
If the session ID is in a hidden form field, a session is
created on the server and the browser has nothing. To use
that session you have to inject the session ID again in each
following request.
Conclusion: with cookies session fixation is -lets say- one
URL, while with hidden fields you need to do it for each
request it should apply to.
If the application renews the session ID after creation, both
methods could considered to be safe.
If the application *does not* renew the session ID after
creation, the threat are cookies only (see above).
I guess I don't understand your point here. An application using
form-based session management would need to pass the session ID back and
forth with every request/response just as if the session ID were being
stored in a cookie. If I execute a form-based session fixation attack,
the fixated session ID will simply get passed back and forth for the
remainder of the session in the same way that a cookie would. Which
brings us back to Brian's point that session fixation is easier when the
application is using form-based session management because I can execute
the attack from anywhere.
!! - 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.
Yep.
Regards,
Tom
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