Spotify ArtistExplorer BB #1 - Cross Site Script Vulnerability

Document Title:
===============
Spotify ArtistExplorer BB #1 - Cross Site Script Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1662


Release Date:
=============
2016-04-17


Vulnerability Laboratory ID (VL-ID):
====================================
1662


Common Vulnerability Scoring System:
====================================
3.5


Product & Service Introduction:
===============================
Start with a seed artist (or genre) and click any artist`s icon to see related artists. Hover over an artist to hear a sample of their music. 
Artist Explorer automatically plays 30 second previews of the top tracks for each artist. This fascinating tool lets you explore relationships 
between over 2,000,000 artists on Spotify and see selected information about them gathered from both the Spotify Web API and the Echo Nest API.
This is one of the main demonstration apps for our developer tools. The source code is available on GitHub.

(Copy of the Vendor Homepage: https://developer.spotify.com/showcase/item/artist-explorer-spotify/ )


Abstract Advisory Information:
==============================
An independent vulnerability laboratory researcher discovered a POST Inject cross site scripting web vulnerability in the Spotify ArtistExplorer web-application.


Vulnerability Disclosure Timeline:
==================================
2016-01-16: Researcher Notification & Coordination (Karim Rahal)
2016-01-17: Vendor Notification (Spotify Security Team)
2016-02-03: Vendor Response/Feedback (Spotify Security Team)
2016-03-20: Vendor Fix/Patch (Spotify Developer Team)
2016-03-25: Security Acknowledgements (Spotify Security Team)
2016-04-09: Security Bulletin (Spotify Security Team) [Acknowledgements]
2016-04-17: Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================
Spotify
Product: ArtistExplorer - Web Application 2016 Q1


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


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


Technical Details & Description:
================================
A persistent cross site scripting web vulnerability has been discovered in the official Spotify ArtistExplorer online service web-application.
The vulnerability allows remote attackers to inject via POST method own malicious script codes on the application-side of the online service.

This vulnerability exists because of a HTML escaping lack and the attack scenerio of this vulnerability is really dangerous! attacker can insert 
malicious code into his artist explorer shared paged and send it to vicitm and maybe steal the victim`s information with his malicious code! 
The Post injection allows an attacker to put modify names, pictures and even the popularity! The request method to inject is POST and the attack 
vector is located on the application-side.

The security risk of the filter bypass and persistent validation vulnerability is estimated as medium with a cvss (common vulnerability scoring 
system) count of 3.5. Exploitation of the persistent input validation web vulnerability requires a low privileged user account with restricted 
access and low or medium user interaction. Successful exploitation of the vulnerability results in session hijacking, persistent phishing, 
persistent external redirects to malicious source and persistent manipulation of affected or connected application modules.

Vulnerable Product(s): 
				[+] Spotify

Affected Service(s):
				[+] Spotify ArtistExplorer (artistexplorer.spotify.com)


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.

Manual steps to reproduce the vulnerability ...
1. Go to https://artistexplorer.spotify.com/
2. Open a Request proxy interpruting/capturing tool like (Live http headers,Tamper data,Burp suite).
3. Then start Capturing/Interpruting the requests
4. Click Share this tree
5. Edit the post content in the captured post request
change {"artist":{"external_urls":{"spotify":"https://spotify/(URL)"} to {"artist":{"external_urls":{"spotify":"javascript:alert('xss')"}
and change any other information like name/popularity (for post injection)
6. Then replay the request
7. A generated number will appear in the replayed page
8. Take the number and put it into "https://artistexplorer.spotify.com?tree=(THE NUMBER)"
Example: https://artistexplorer.spotify.com?tree=62e35fe55f3b452b9d9cb0334eaa1f5d
9. Then click on the first artist in the tree, and then you will see artist info in the sidebar, click on his name and tadaa! XSS will popup! And if you changed anything else for post injection purposes like Popularity/artist name, you will it has been done!
10. Successful reproduce of the vulnerability!

Video: https://www.youtube.com/watch?v=x0vLyb91PPI


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure parse and encode of the vulnerable `tree` values in the artistexplorer.
Restrict the input and disallow usage of special chars on input. Prevent an execution of script code by implementation of an exception-handling.


Security Risk:
==============
The security risk of the POST inject web vulnerability in the Spotify ArtistExplorer web-application is estimated as medium. (CVSS 3.5)


Credits & Authors:
==================
Karim Rahal - @KarimMTV [http://www.vulnerability-lab.com/show.php?user=Karim%20Rahal]


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