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Prezi Bug Bounty #7 - (Charts) Persistent Vulnerability

2016-02-23 09:40
Document Title:
Prezi Bug Bounty #7 - (Charts) Persistent Vulnerability

References (Source):

Release Date:

Vulnerability Laboratory ID (VL-ID):

Common Vulnerability Scoring System:

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:
The Vulnerability Laboratory Research team discovered an application-side input validation web vulnerability in the
official Prezi online service web-application.

Vulnerability Disclosure Timeline:
2016-01-27: Researcher Notification & Coordination (Milan Solanki)
2016-01-27: Vendor Notification (Prezi.com Security Team - Bug Bounty Program)
2016-02-02: Vendor Fix/Patch (Prezi.com Developer Team)
2016-02-23: Public Disclosure (Vulnerability Laboratory)

Discovery Status:

Affected Product(s):
Product: Online Service - Web Application 2015 Q4

Product: Online Service - Web Application 2016 Q1

Exploitation Technique:

Severity Level:

Technical Details & Description:
An application-side cross site scripting web vulnerability has been discovered in the official Prezi online service
The security vulnerability allows remote attackers to inject own script code to the application-side of the affected
application module.

The vulnerability is located in the presentation charts function on Prezi online service web application. Remote
attackers with low privilege
web-application user accounts are able to inject own malicious script code via POST method request. The injection point
is the vulnerable
charts data field. The request method to inject is POST and the vulnerability is located to the application-side of the
vulnerable service.

The security risk of the application-side cross site vulnerability is estimated as medium with a cvss (common
vulnerability scoring system) count of 3.9.
Exploitation of the persistent input validation web vulnerability requires a low privilege web-application user account
and low or medium user interaction.
Successful exploitation of the vulnerability results in session hijacking, persistent phishing attacks, persistent
external redirects to malicious source
and persistent manipulation of affected or connected application modules.

Proof of Concept (PoC):
The security vulnerability can be exploited by remote attackers with low privilege web-application user account and low
or medium user interaction.
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to

PoC: Payload
<--`<img/src=` onerror=alert(document.cookie)> --!>

Manual steps to reproduce the vulnerability ...
1. Create new presentation
2. Select the charts function
3. Go to Data Field
4. There are 4 function by default (online, email, seo & social)
5. Save the cross site scripting payload as the chart
6. Save the presentation and send to the victim
7. Victim try to re-edit the chart and visit the Data field
8. Thats it XSS executed In victim account also

Solution - Fix & Patch:
The vulnerability can be patched by a secure parse and encode of the vulnerable fields. Restrict the input and disallow
usage of special chars.
Filter and setup a secure exception handling that prevents the persistent execution in the output location.

Security Risk:
The security risk of application-side input validation web vulnerability in the frontend of the Prezi web-application
is estimated as medium. (CVSS 3.9)

Credits & Authors:
Milan Solanki - [http://www.vulnerability-lab.com/show.php?user=Milan%20A%20Solanki]

Disclaimer & Information:
The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all
warranties, either
expressed or implied, including the warranties of merchantability and capability for a particular purpose.
Vulnerability-Lab or its suppliers
are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or
special damages, even
if Vulnerability-Lab or its suppliers have been advised of the possibility of such damages. Some states do not allow
the exclusion or limitation
of liability for consequential or incidental damages so the foregoing limitation may not apply. We do not approve or
encourage anybody to break
any vendor licenses, policies, deface websites, hack into databases or trade with fraud/stolen material.

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