Prezi Bug Bounty #5 - Client Side Cross Site Scripting & Open Redirect Vulnerability

[Vulnerability Lab <research@xxxxxxxxxxxxxxxxxxxxx>]

Document Title:
===============
Prezi Bug Bounty #5 - Client Side Cross Site Scripting & Open Redirect 
Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1724


Release Date:
=============
2016-02-19


Vulnerability Laboratory ID (VL-ID):
====================================
1724


Common Vulnerability Scoring System:
====================================
3


Product & Service Introduction:
===============================
Prezi is a cloud-based presentation software based on a software as a service 
model. The product employs a zooming user interface (ZUI), which allows 
users to zoom in and out of their presentation media, and allows users to 
display and navigate through information within a 2.5D or parallax 3D space 
on the Z-axis. Prezi was officially established in 2009 by co-founders Adam 
Somlai-Fischer, Peter Halacsy and Peter Arvai.

(Copy of the Wikipedia entry: https://en.wikipedia.org/wiki/Prezi)


Abstract Advisory Information:
==============================
An independent vulnerability laboratory researcher discovered a client-side 
redirect web vulnerability in the official Prezi web-application.


Vulnerability Disclosure Timeline:
==================================
2016-00-29: Researcher Notification & Coordination (Milan Solanki)
2016-00-30: Vendor Notification (Prezi Security Team)
2016-00-04: Vendor Response/Feedback (Prezi Security Team)
2016-00-16: Vendor Fix/Patch #1 (Prezi Developer Team)
2016-00-22: Security Acknowledgements (Prezi Security Team)
2016-00-17: Security Bulletin  (Prezi Security Team)
2016-00-18: Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================
Prezi
Product: Online Service - Web Application 2016 Q1


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


Severity Level:
===============
Medium


Technical Details & Description:
================================
An open redirect web vulnerability has been discovered in the official Prezi 
web-application.
The bug allows remote attackers to execute external urls by the internal 
web-application requests via client-side.

The vulnerability is located in the GET parameter of the vulnerable `track` 
module. The vulnerability allows an remote 
attacker to prepare client-side malicious urls to external sources. The request 
method to execute is GET and the vulnerability is 
located on the application-side of the online-service. The vulnerability is a 
classic open redirect web vulnerability.

The security risk of the open redirect web vulnerability is estimated as medium 
with a cvss (common vulnerability scoring system) count of 3.0. 
Exploitation of the persistent input validation web vulnerability requires no 
privileged user account and low or medium user interaction. 
Successful exploitation of the vulnerability results in client-side redirects 
to malicious sources or client-side phishing.

Request Method(s):
                                [+] GET

Vulnerable Module(s):
                                [+] /track

Vulnerable Parameter(s):
                                [+] URI


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

Vulnerability:
Open redirect in the following module:  
/track?type=click&enid=[UNIQUE-ID]&&&2003&&&http://EVILURLHERE.com

PoC:
click.prezi.com/track?type=click&enid=ZWFzPTEmbXNpZD0xJmF1aWQ9ODMxNDk0MjImbWFpbGluZ2lkPTM2NzMmbWVzc2FnZWlkPTExNyZkYXRhYmFzZWlkPTE0NTAxMzM4Njkmc2VyaWFsPTE2Nzc3NTIzJmVtYWl
saWQ9bWFzaGFjazQyM0BnbWFpbC5jb20mdXNlcmlkPTFfMTU1MTYzJnRhcmdldGlkPSZtbj04MTE1NDQmZmw9Jm12aWQ9JmV4dHJhPSYmJg==&&&2003&&&https://facebook.com


Solution - Fix & Patch:
=======================
Disallow to request not whitelisted webpages and include a tag filter to the 
enid to prevent as well.
Restrict and filter the parameter and disallow usage of special chars. Encode 
the GET request to prevent client-ide script code inject.


Security Risk:
==============
The security risk of the client-side open redirect web vulnerability in the 
Prezi web-application is estimated as low. (CVSS 3.0)


Credits & Authors:
==================
Milan A Solanki - (milans812@xxxxxxxxx) 
[http://www.safehacking4mas.blogspot.in] [https://www.facebook.com/Mas.Hackers]


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