usabilty vs sescurity - return urls by parameter

["MC Iglo" <mc.iglo () googlemail com>]

Hi all,

lately, I see more and more pages using get-parameters to store a
return url after login.
two famous examples are ebay and google.

of course, this is nice for the user to get back to where he came from
before logging in.
but on the other hand side, i think thats an extremly high risk!

in most cases, the URL is something like
http://gooddomain.tld/login.php?arg1=bla&arg2=blaaaaaaa&arg3=%22alb%22&return=http%3A%2F%2Fgooddomain.tld%2Fadmin&morearg=morebla



As you can see at the upper example, it is not very clear, what URL the
user will be redirected to.
Now lets obfuscate it a little bit more and replace the return path and you get
http://gooddomain.tld/login.php?arg1=bla&arg2=blaaaaaaa&arg3=%22alb%22&return=%68%74%74%70%3a%2f%2f%62%75%67%67%65%6c%7a%2e%66%75%6e%70%69%63%2e%64%65%2f%67%70%6f%74%61%74%6f%2e%68%74%6d%6c&morearg=morebla

(The decoded string is an example form - I notified them seperatley before)

let's send this link to someone interested in their products or put it
on a website/forum as a reply to a question. Even careful people might
be tricked to click on this link and log in because they see
'http://gooddomain.tld/...'. and that IS the site, they want to go
to.
after they logged in successfully, the website redirects them to my
malicious site, which says, the login was incorrect. of course, the
user will not be distrustful beause he was sent to this 'view' by
gooddomain.tld (he
won't check the address bar for sure) and type in his data again to be
sure, he made no typos and i store this data on my server
i have successfully stolen his data and redirect him to the normal portal.
he won't even notice it and thinks he made a typo at first try.

in my opinion, this is extremely critical
but hey... who cares? it's web 2.0...

Regards
MC.Iglo

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