Skype 2.8.x & 5.3.x - Memory Corruption Vulnerability

Document Title:
===============
Skype 2.8.x & 5.3.x - Memory Corruption Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=180
CNNVD-201110-710 > http://www.cnnvd.org.cn/vulnerability/show/cv_id/2011100710


Release Date:
=============
2011-08-22


Vulnerability Laboratory ID (VL-ID):
====================================
180


Product & Service Introduction:
===============================
Skype is a famous 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. 
In 2011 Microsoft bought the skype company & the software is now a official microsoft product.

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


Abstract Advisory Information:
==============================
Vulnerability-Lab team discovered a memory corruption vulnerability on the Skype VoIP v5.3.x, v2.8.x & v5.1.x software.


Vulnerability Disclosure Timeline:
==================================
2011-07-02:	Vendor Notification
2011-07-04:	Vendor Response/Feedback
2011-07-24:	Vendor Fix/Patch
2011-08-22:	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:
=======================
Local


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


Technical Details & Description:
================================
A critical pointer vulnerability is located in the macosx & windows version of skype. The bug/vulnerability is located in 
2 input forms of an uni-code http search request to the skype search directory server. The vulnerability allows an local attacker 
to crash the complete skype process via an unknown unhandled software exception(memory-corruption). Successful exploitation of 
the bug can lead to local system compromise by overwriting on a machine specific memory address.

Vulnerable Module(s):
						[+] Input Mask - Geschäftsempfehlungen finden - Wo? & Was?


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




Pictures:
						../1.png
						../2.png
						../skype_debug_win7_x64x.png
						../skype_debug2_win7_x64x.png
						../skype_error_mac_osx_x64x.tiff
						../unhandled-exception_win7_x64.png


Proof of Concept (PoC):
=======================
The vulnerability can be exploited by local attackers. For demonstration or reproduce ...

Manually reproduce ...

1. Install Skype Software
2. Register an Account
3. Login & switch to the search Menu "Geschäftsempfehlungen finden - Wo? & Was?"
4. Include a emtpy long zero-string or a long uni-code string like AAAAAAAAA+ on the input mask (1.png)
5. Switch to immunity or windbg & catch the process (skype_debug_win7_x64x.png)
6. Execute the input of the mask ... & feel free (1.png)
7. An unhandled & unknown exception get droped and the software crashs via memory-corruption by an pointer bug
7. Read & write after local exploitation like ... skype_debug2_win7_x64x.png ... is possible :)


Analyses:
				../debug_log_win7.txt


Solution - Fix & Patch:
=======================
2011-07-24:	Vendor Fix/Patch - Skype decided to exclude the skype user directory


Security Risk:
==============
The security risk of the local exploitable memory corruption vulnerability is estimated as medium.


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


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