Skype 5.3.x 2.2.x 5.2.x - Persistent Software Vulnerability

Document Title:
===============
Skype 5.3.x 2.2.x 5.2.x - Persistent Software Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=182
CNNVD-201110-709 > http://www.cnnvd.org.cn/vulnerability/show/cv_id/2011100709


Release Date:
=============
2011-09-05


Vulnerability Laboratory ID (VL-ID):
====================================
182


Product & Service Introduction:
===============================
Skype is a software application that allows users to make voice and video calls and chats over the Internet. Calls to other users within the
Skype service are free, while calls to both traditional landline telephones and mobile phones can be made for a fee using a debit-based
user account system. Skype has also become popular for its additional features which include instant messaging, file transfer, and
videoconferencing. Skype has 663 million registered users as of 2010.  The network is operated by Skype Limited, which has its headquarters
in Luxembourg. Most of the development team and 44% of the overall employees of Skype are situated in the offices of Tallinn and Tartu, Estonia.

(Copy of the Vendor Homepage: http://en.wikipedia.org/wiki/Skype)


Abstract Advisory Information:
==============================
The Vulnerability-Lab Team discovered a persistent software vulnerability in the main module of the Skype software.
The vulnerability is OS independent & has been successfully reproduced by the skype security team on windows7, macos and linux.


Vulnerability Disclosure Timeline:
==================================
2011-07-07:	Vendor Notification
2011-07-09:	Vendor Response/Feedback
2011-09-01:	Vendor Fix/Patch 
2011-10-13:	Public or Non-Public Disclosure



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


Affected Product(s):
====================
Microsoft Corp.
Product: Skype - Software Client 5.3.x 2.2.x 5.2.x


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


Severity Level:
===============
High


Technical Details & Description:
================================
A persistent input validation vulnerability is detected on the windows, linux & macosx version of skype. The bug is located in the status bar 
module of the message index. The vulnerability allows an local attacker to implement persistent malicious script codes on a skype 
software main module. The successfully exploitation can lead to redirects, client exploitation, session hijacking, malicious downloads 
& request manipulation over the vulnerable software main module.

Vulnerable Module(s):
								[+] Status Message Index - Username Output

Exploited via:
								[+] Skype Manager Service


Verified on OS:
								[+] Windows 
								[+] MacOS
								[+] Linux


Affected OS version(s):
								Windows v5.3.0.120 & older versions
								MacOS v5.2.0.1523 & older versions
								Ubuntu v2.2.0.35 & older versions
								Debian v2.2.0.35-1 & older versions
								Fedora v2.2.0.35-f & older versions
								Suse v2.2.0.35-s & older versions

Picture(s):
								../1.png

Picture(s):
								../skype(server2).png


Proof of Concept (PoC):
=======================
The vulnerability can be exploited by remote attackers. Successful exploitation requires to accept a manager invite 
& then for the manager administrator to attack the victim person. For demonstration or reproduce ...


Technique(s): 
Install Skype Software 
=> Login to Skype 
=> Register 2 Skype Manager 
=> Check Status Message Bar 
=> Skype Manager Login2 
=> Change Username input via Update function to script code 
=> Cancel Service 
=> Re-display in Status Message Bar - Execution Local 
=> Invite Victim to Manager Service as Admin 
=> Remote execution of malicious persistent script code

Manually ...
1.  Install Skype Software
3.  Login to your Skype
4.  Now register with the free Skype Manager Service as -> testerX041
5.  Check the skype status message bar if the registrationw was successful
6.  Go to the manager website and login with your user profile
7.  Change your username to malicious test script code under 50 chars(restriction) and save/update the profile
8.  Now cancel the manager service to get a new status message on the skype bar with the malicious tag
9.  After refresh or new software start the persistent script-code gets executed out of the skype main module context (status messages)
10. Invite the remote victim via skype manager to execute the persistent script code out of the victims software context.

Note: Skype disallow the registration with tags ... but when registered you can change to them.
The same method allows an attacker also to stream malicous persistent script code via other
status message outputs like facebook (inbound - integration).

Picture(s):
								../skype(server2).png


Solution - Fix & Patch:
=======================
Validate the user name on the software status message output index on the main module.
Restrict the entry/input of malicious tags on bound services like skype manager.

2011-09-01:	Vendor Fix/Patch  (Attack vector has been removed by Skype!)


Security Risk:
==============
The security risk of the persistent software vulnerability is estimated as high.


Credits & Authors:
==================
Vulnerability Research Laboratory - Benjamin Kunz Mejri (Rem0ve)


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