Skype v5.3.x v2.2.x v5.2.x - Denial of Service Vulnerability

Document Title:
===============
Skype v5.3.x v2.2.x v5.2.x  - Denial of Service Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=181


Release Date:
=============
2011-07-27


Vulnerability Laboratory ID (VL-ID):
====================================
181


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:
==============================
Vulnerability-Lab team discovered a local & remote Denial of Service Vulnerability on the Skype v5.3.x v2.2.x v5.2.x



Vulnerability Disclosure Timeline:
==================================
2011-07-06:	Vendor Notification
2011-07-08:	Vendor Response/Feedback
2011-07-20:	Vendor Fix/Patch
2011-07-28:	Public or Non-Public Disclosure


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


Affected Product(s):
====================

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


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


Technical Details & Description:
================================
A stable denial of service vulnerability is located in the windows version of skype. The Bug is located in the notification 
module of the Benachrichtigungsoptionen. The vulnerability allows an local attacker to crash the complete skype process via 
APPHang(application-hang) & APPCrash. The bug allows an local attacker to block the users message board by including on the 
savebox a  %long<string>+[Space]+%long<string> message. The input field of the notifification-option has no size restriction 
as maximum. After including the software ever asks ifself on every keyboard attempt ... whats inside? The result is in a stable 
denial of service apphang & appcrash ... also after a restart because its saved. ;) 


Vulnerable Module(s):
								[+] Benachrichtigungsoptionen - Word Notification Setting

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


Affected OS version(s):
								Windows v5.3.0.120, 5.4.x, 5.5.x & 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):
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Proof of Concept (PoC):
=======================
The vulnerability can be exploited by local attackers. For demonstration or reproduce ...

Technique(s):
=> Install 
=> Login 
=> Choose Username
=> Insert large String
=> Persistetn Weakness on view of profile or message sending
=> After insert the vulnerability is exploitable from local techique to remote

Manually reproduce ...
1. Install Skype Software
2. Register an Account
3. Login, click on a user in the bar
4. Switch to the Notificationoptions on the skype top menu
5. Check on the last box were "Nur benachrichten wenn wörter geschrieben wurden" is located
6. Implement  >  %long<string>+[Space]+%long<string>
7. Save the Configuration
8. Now the bug can be exploited via inter action of remote attacker by sending you 1 charakter

Analyses:
		../AppHang_Skype.exe_2794e078fd2583f9c2d7ba5fcfdd99371f461cb1_01caed60
		../AppHang_Skype.exe_97123e82cc7a24daaf86b37f05b6fe7cb2ac0c5_15c6a1b2
		../AppHang_Skype.exe_ac6288b29d34cbca057010ebc6e75853ea6767_0a087798
		../AppHang_Skype.exe_d3339b31fc3e889da580a3304baee6ec8eaad66_056c3c3c
		../AppHang_Skype.exe_d3339b31fc3e889da580a3304baee6ec8eaad66_0367ba7f
		../AppHang_Skype.exe_de34bcdc54d51498c88c883af18b128304e38f2_15c45d14
		../skype-debug_access-violation2.txt


Solution - Fix & Patch:
=======================
2011-10-**:	Vendor Fix/Patch (Fix will be provided soon!)


Security Risk:
==============
The security risk of the vulnerability is estimated as medium because its a stable software crash without secure exception-handling.


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


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