Title:
======
Skype Community - Mail Encoding Web Vulnerability #1


Date:
=====
2012-11-20


References:
===========
http://www.vulnerability-lab.com/get_content.php?id=708

MICROSOFT SECURITY RESPONSE CENTER (MSRC) ID: [13021bc]


VL-ID:
=====
708


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


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:
=========
The Vulnerability Laboratory Research Team discovered a filter & mail encoding vulnerability in the official Skype Community Website Application.


Report-Timeline:
================
2012-09-28:  Researcher Notification & Coordination
2012-09-30:  Vendor Notification
2012-10-02:  Vendor Response/Feedback
2012-11-18:  Vendor Fix/Patch
2012-11-21:  Public or Non-Public Disclosure


Status:
========
Published


Affected Products:
==================
Microsoft
Product: Community (Forums) 2012 Q3-4


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


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


Details:
========
A filter and mail encoding vulnerability is detected in the official Skype Community Website Application.
The vulnerability is located in the not sanitized message body and title parameters when processing to load the 
bound vulnerable Problem Reporter or Send to Friends module. The vulnerability affects the later outgoing mails service 
and allows execution of persistent script codes against admins, moderators or customers of the forum. The script code get 
executed out of the message itself inside of the main mail template. Successful exploitation of the vulnerabilities result in 
persistent phishing mails, persistent session hijacking attacks and persistent mail web context manipulation via skype website.

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

Vulnerable Module(s):
        [+] Problem Reporter & Send to Friends

Vulnerable Parameter(s):
        [+] Message Body & Title (says)

Affected:
        [+] Notification Mail (outgoing)


Proof of Concept:
=================
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 ...

Send to Friends:
http://community.skype.com/t5/notifications/notifymoderatorpage/message-uid/1062818
http://community.skype.com/t5/notifications/emailmessagepage/board-id/de_computer_windows/message-id/6304

Problem Reporter:
http://community.skype.com/t5/notifications/notifymoderatorpage/message-uid/1075268

Support:
https://support.skype.com/de/support_request_form?needsLogin=true&topic=6270000000026383241&problem=6270000000028975692


PoC:

<html><head>
<title>Einladung zum Besuch bei Skype Support Network</title>
<link rel="important stylesheet" href="chrome://messagebody/skin/messageBody.css">
</head>
<body>
<table class="header-part1" border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr>
<td><b>Betreff: </b>Einladung zum Besuch bei Skype Support Network</td></tr><tr><td><b>Von: </b>
rm01x <admin@vulnerability-lab.com></td></tr><tr><td><b>Datum: </b>Tue, 25 Sep 2012 15:32:34 -0700 (PDT)
</td></tr></tbody></table><table class="header-part2" border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><b>An: 
</b>01x445 <01x445@gmail.com></td></tr></tbody></table><br>
  
<title> Einladung zum Besuch bei Skype Support Network </title>

rm01x (admin@vulnerability-lab.com) bei Skype Support Network findet es faszinierend, hilfreich, interessant, nützlich, 
provozierend, zum Nachdenken anregend oder einfach cool. Wir hoffen, Sie besuchen Skype Support Network und schauen es 
sich mit eigenen Augen an. <p>  <a href="http://community.skype.com/skypec/board/message?board.id=de_computer_windows
&message.id=6304#M6304">http://community.skype.com/skypec/board/message?board.
id=de_computer_windows&message.id=6304#M6304</a>  </p>
    <p>  rm01x sagt: </p>
    <p> >"<[PERSISTENT INJECTED MALICIOUS SCRIPT CODE!]/">



Note:
The attacker can send the code via `send to friends` to hijack customer accounts or via problem reporter to a moderator or administrator of 
the skype community. The script code will be executed directly out of the unsanitized message body of the mail. The vulnerability also exists 
in the skype main server when requesting via automatically help or contact forms. The outgoing mail with the malicious script code as values 
can be send to users/customers or to the moderator/administrator. 


Reference(s):
        ../references.txt
        ../Einladung zum Besuch bei Skype Support Network.html
        ../Einladung zum Besuch bei Skype Support Network.eml


Solution:
=========
The vulnerability can be patched by parsing the message context of the send to friends or problem reporter module.
Restrict the input forms of the contact or problem report formulars [A-Z][a-z][0-9] to remove the attack vector.


Risk:
=====
The security risk of the filter encoding and validation vulnerability is estimated as medium(+).


Credits:
========
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (bkm@vulnerability-lab.com)


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===========
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