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[Full-disclosure] RCSR fun: stealing FF passwords the easy way

From: pagvac (unknown.pentestergmail.com)
Date: Fri Nov 24 2006 - 07:41:55 CST

RCSR (Reverse Cross-Site Request) attacks discovered by Robert Chapin,
make the theft of passwords in Firefox extremely trivial. I encourage
you to try the attack as it can be kind of a shocking experience.


1. User logs into www.target.com through a typical HTML login form

2. Firefox asks the user if he/she wants to save the password -
provided that FF never asked the user to save the password for that
site before ("Remember passwords for sites" under "Options/Security"
must be *enabled*)

3. Victim user clicks on "Remember"

4. Victim user accesses an HTML page on www.target.com containing an
injected HTML form with the username and password input names *equal*
to the legitimate login form from step 1

5. Firefox fills out automatically the form with the original username
and password values

6. Victim user clicks on a malicious link

7. Credentials get sent to evil site!

Now, the form can be completely invisible by adding a bit of HTML to
the form inputs. I managed to create a form in which all you need is
trick the victim user to click on an image.

Attack walk through:

1. Enter any fake credentials on
http://ikwt.com/projects/RCSR/legit_form.html and click on "Login"

2. If "Remember passwords for sites" is enabled, FF should prompt you
to save the password.

3. Click on "Remember"

4. Now, in order to illustrate that FF will automatically fill in the
credentials on any form located on the same site which uses input
names *equal* the the legitimate form access the following URL:


If it worked, you should see the username and password field filled in
automatically by FF. Of course, an evil form like this looks very
suspicious, but this is just an example to make the point that FF
trusts and fills in the form simply because it's located on the same
site and uses input names equal to the legitimate form.

Now, in order to make our evil form more effective we just added the
following line the in the username and password fields:

style="display: none;"

Finally, we change our submit button for an image that will make a
good bait. In this case we choose beautiful Scarlett Johansson :-)

If you click on the image, you should see your credentials forwarded
to Google within the URL:


The beauty of this attack is that we don't need JavaScript, it's all
plain HTML tags. Also, there is *no* patch yet. Apparently this has
been widely exploited on myspace. I recommend everyone to research
this attack as it's highly exploitable on sites in which users can
insert HTML - either though legitimate features (i.e.: posts) or by
exploiting security bugs such as HTML injection


- tested successfully on Mozilla Firefox 2.0
- JavaScript can also be used to exploit this vulnerability through
the 'submit()' method (only visiting the evil page is required in this

Check out the following links for more info:

http://www.kriptopolis.org/robo-de-contrasenas-en-firefox (in Spanish)


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