Skype Community - Persistent Editor Web Vulnerability

Document Title:
===============
Skype Community - Persistent Editor Web Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=707

MICROSOFT SECURITY RESPONSE CENTER (MSRC) ID:  13021bc


Release Date:
=============
2013-03-28


Vulnerability Laboratory ID (VL-ID):
====================================
707


Common Vulnerability Scoring System:
====================================
4


Product & Service Introduction:
===============================
Skype is a proprietary voice-over-Internet Protocol service and software application originally created in 2003 by Swedish entrepreneur 
Niklas Zennström and his Danish partner Janus Friis. It has been owned by Microsoft since 2011. The service allows users to communicate 
with peers by voice, video, and instant messaging over the Internet. Phone calls may be placed to recipients on the traditional telephone 
networks. Calls to other users within the Skype service are free of charge, while calls to landline telephones and mobile phones are charged 
via a debit-based user account system. Skype has also become popular for its additional features, including file transfer, and videoconferencing. 
Competitors include SIP and H.323-based services, such as Linphone, as well as the Google Talk service, Mumble and Hall.com.

Skype has 663 million registered users as of September 2011. The network is operated by Microsoft, which has its Skype division headquarters 
in Luxembourg. Most of the development team and 44% of the overall employees of the division are situated in Tallinn and Tartu, Estonia.

Unlike most other VoIP services, Skype is a hybrid peer-to-peer and client–server system. It makes use of background processing on computers 
running Skype software. Skype`s original proposed name (Sky Peer-to-Peer) reflects this fact. Some network administrators have banned Skype 
on corporate, government, home, and education networks, citing reasons such as inappropriate usage of resources, excessive bandwidth usage, 
and security concerns.

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


Abstract Advisory Information:
==============================
The Vulnerability Laboratory Research Team discovered a persistent web vulnerability in the official Skype Community Website Application.


Vulnerability Disclosure Timeline:
==================================
2012-09-26:	Researcher Notification & Coordination
2012-09-28:	Vendor Notification
2012-10-02:	Vendor Response/Feedback
2013-02-22:	Vendor Fix/Patch by Check
2013-03-29:	Public Disclosure


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


Affected Product(s):
====================
Microsoft Corp.
Product: Skype Community - Lithium Forums 2012 Q3


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


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


Technical Details & Description:
================================
Multiple persistent input validation vulnerabilities are located in the official Skype Community Website Application.
The bug allows remote attackers with low account privileges to inject via editor & replace function own malicious 
persistent script code. The vulnerabilities are located in the forum editor module with the replace function and the 
bound vulnerable message titel, subject and link parameters. Remote attackers can compose malicious forum posts to 
hijack admin/moderator/customer accounts. Successful exploitation result in local persistent web context manipulation, 
client side phishing or persistent session hijacking via forum messages.


Vulnerable Section(s):
				[+] Skype Community (Forums) - Lithium Forum

Vulnerable Module(s):
				[+] Editor (in combination with the replace all function to execute)

Vulnerable Parameter(s):
				[+] Message Subject, Topic Title & Link


Proof of Concept (PoC):
=======================
The vulnerability can be exploited by remote attackers with low or medium required user inter action and with skype application service user account. 
For demonstration or reproduce ...


PoC:

<ul id="list_0" class="lia-list-standard-inline">
<li class="tag-35234 lia-tag-list-item"><a class="lia-link-navigation lia-tag tag tag-35234 
lia-js-data-tagUid-35234" rel="tag" id="link_10" href="/t5/tag/[PERSISTENT INJECTED MALICIOUS SCRIPT CODE!]/tg-p/
board-id/de_general">>"<iframe src=vulnerabi…</a><div class="tag-list-js-confirmation hidden"></div></li>
</ul>
	


... or


<div class="lia-form-row lia-form-subject-entry">
		
<div class="lia-form-label-wrapper">				
<label for="lia-subject" class="lia-form-label">Betreff</label>
				
</div>
		
<div class="lia-quilt-row lia-quilt-row-standard">
	
<div class="lia-quilt-column lia-quilt-column-24 lia-quilt-column-single">
	<div class="lia-quilt-column-alley lia-quilt-column-alley-single">
		
<div class="lia-form-input-wrapper">
								
<input style="" class="lia-form-subject-input lia-form-type-text lia-form-input-vertical" 
maxlength="2000" value="Betreff: Sicherheitsfrage" id="lia-subject" name="subject" type="text">
			
</div>
			
	</div>
</div>
		
		
</div>
	
</div>	
<div class="lia-inline-ajax-feedback">
<div style="display: none;" class="AjaxFeedback" id="savedAutosaveFeedback"></div>
			
		</div>

		<div class="lia-inline-ajax-feedback lia-saved-autosave-feedback"><a shape="rect" name="feedback-success"> </a>
	
<div class="InfoMessage lia-panel-feedback-inline-note lia-component-common-widget-feedback" id="feedback_13a00ba6edd_2da38">
			<div class="lia-text">
					
				<p>Automatisch speichern unter 5:59 AM </p>

			</div>
		</div></div>

				<div class="MessageEditor" id="messageEditor">
	<div class="lia-form-row lia-form-body-entry">

			<div class="lia-form-label-wrapper">				
				<label for="tinyMceEditor" class="lia-form-label">Text</label>
				
			</div>



Reference(s):
http://community.skype.com/t5/forums/replypage/board-id/de_general/message-id/5695


Reference(s):
				../index.dat
				../5695.htm
				../5695-2.htm


Solution - Fix & Patch:
=======================
The vulnerability can be patched by parsing the message web context of subject, title & link in the lithium forum editor.
Parse the web context of the replace input form and restrict the input or prevent execution via own secure exception-handling.


Security Risk:
==============
The security risk of the input validation vulnerabilities are estimated as medium(+).


Credits & Authors:
==================
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri ([email protected])


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