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AUSCERT External Security Bulletin Redistribution
ESB-2008.0097 -- [Win]
Skype Cross Zone Scripting Vulnerability
29 January 2008
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AusCERT Security Bulletin Summary
---------------------------------
Product: Skype 3.5.x and 3.6.x
Publisher: Skype
Operating System: Windows
Impact: Execute Arbitrary Code/Commands
Access: Remote/Unauthenticated
CVE Names: CVE-2008-0454
Original Bulletin: http://skype.com/security/skype-sb-2008-001-update1.html
http://skype.com/security/skype-sb-2008-001-update1.txt
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________________________________________
SKYPE SECURITY BULLETIN SKY-CERT
Bulletin title: Skype Cross Zone Scripting Vulnerability
Bulletin ID: SKYPE-SB/2008-001
Bulletin status: PRELIMINARY
Date of announcement: 2008-01-23 9:00:00 +0000
Products affected: Skype for Windows
Vulnerability type: Code injection
CVE references:
Risk assessment: HIGH
CVSS base score: 10.0
(AV:N/AC:L/Au:N/C:C/I:C/A:C)
Cross-references:
http://aviv.raffon.net/2008/01/17/SkypeCrosszoneScriptingVulnerability.aspx
http://seclists.org/fulldisclosure/2008/Jan/0328.html
Table of contents:
1. Problem description and brief discussion
2. Impact and affected software
3. Solution or work-around
4. Special instructions and notes
5. Software download location
6. Authenticity verification
7. Common Vulnerability Scoring System (CVSS) assessment
8. Credits and additional information
9. Bulletin release history
10. Notices
________________________________________________________________________
1. Problem description and brief discussion
Description
-----------
Skype uses Internet Explorer web control to render HTML content.
This is used also for providing "add video to mood" and
"add video to chat" functionality.
This is realized over JS/ActiveX interface which allows scripts
to be run in Local Zone security context of IE.
In order to exploit this an attacker must exploit code injection
vulnerability at the partner site. Such vulnerability has been
discovered in Dailymotion website.
Similar vulnerability has been now detected also in Metacafe Pro
video submission software.
Discussion
----------
An attacker who constructs a Title of the video in a specific way
in the Dailymotion gallery can cause arbitrary code to be executed
on targets PC. For the vulnerability to be triggered, the target
must find this video in Skype video gallery browser section. Watching
the video in a Skype chat or in a mood message is safe, as Internet
Explorer control is not used.
Details of vulnerability in Metacafe have not been disclosed. However
the PoC has been enhanced in a way which enables to refer to the
malicious video through a Skype uri which in turn can be sent directly
to victims.
The proof of concept has been published by Aviv Raff and Miroslav
Lucinskij.
________________________________________________________________________
2. Impact and affected software
Impact
------
A user of Skype for Windows, who has his/her Skype running and
follows a link to specially crafted video may experience execution
of arbitrary code without consent.
Affected Software
-----------------
The following Skype clients are vulnerable to this attack:
Skype for Windows:
All releases including 3.5.* and 3.6.*
________________________________________________________________________
3. Solution or work-around
Skype has temporarily disabled users' ability to browse videos from
Dailymotion's gallery until an official fix has been made available.
Skype has now fully disabled video adding from gallery until an
official fix has been made available.
________________________________________________________________________
4. Special instructions and notes
None.
________________________________________________________________________
5. Software download location
The preferred method for installing security updates is to download
the software directly from Skype's website, from the website of
Skype's authorized partners, or from a reliable mirror site. Skype
may also be safely downloaded from other locations, but in this
case it is particularly important that you verify the authenticity
of the download.
We recommend that once you download any Skype software that you
verify its integrity by the methods listed in Section 6 of this
Bulletin.
x86 platform, Microsoft Windows 2000 or Microsoft Windows XP:
http://www.skype.com/products/skype/windows/
x86 platform, Linux:
http://www.skype.com/products/skype/linux/
PPC and x86 platforms, Mac OS X v10.3.9 or later:
http://www.skype.com/products/skype/macosx/
Pocket PC platform, Microsoft Windows Mobile 2003:
http://www.skype.com/products/skype/pocketpc/
________________________________________________________________________
6. Authenticity verification
- Bulletin authenticity verification:
Skype security bulletins are published on Skype's web site and
via mailing lists. The authenticity and integrity of a Skype
security bulletins may be determined by inspecting the crypto-
graphic signature that is attached to each bulletin. All Skype
security bulletins are published with a valid digital signature
produced by PGP.
- Software authenticity verification:
Both the Skype installer program and the Skype program that is
installed by the installer are digitally signed.
For Skype software built for Microsoft Windows and Mac OSX operating
environments, the digital certificate used by Skype to sign
software packages is signed by "VeriSign Class 3 Code Signing 2004
CA".
For Skype software built for Linux platforms, all packages are
signed by PGP key ID 0xD66B746E, the public component of which may
be downloaded from http://www.skype.com/products/skype/linux/.
- For general information about Skype security, please visit the
Skype Security Resource Center at http://www.skype.com/security/.
________________________________________________________________________
7. Common Vulnerability Assessment System (CVSS) assessment
Skype has rated the issue covered by this Security Bulletin under
the CVSS scheme as follows:
Base metrics as of 2008-01-23:
Access Vector (AV) ........... Network
Access Complexity (AC) ....... Low
Authentication (Au) .....,.... Not Required
Confidentiality Impact (C) ... Complete
Integrity Impact (I) ......... Complete
Availability Impact (A) ...... Complete
Computed CVSS base score: 10.0
Temporal metrics as of 2008-01-23
Exploitability (E) ........... Functional
Remediation Level (RL) ....... Workaround
Report Confidence (RC) ....... Confirmed
Computed CVSS temporal score: 9.0
Skype participates in the CVSS by rating each identifiable security
vulnerability against the CVSS base metrics. In addition, Skype
may rate each vulnerability against temporal metrics from time to
time. As suggested by the name, temporal metrics for a particular
vulnerability may change from time to time.
More information about the CVSS may be obtained from the CVSS host
website at http://www.first.org/cvss/.
________________________________________________________________________
8. Credits and additional information
Skype would like to thank and credit Aviv Raff for having referred
this problem to Skype.
________________________________________________________________________
9. Bulletin release history
2008-01-18 Initial bulletin release
2008-01-23 Bulletin updated
________________________________________________________________________
10. Notices
Copyright 2006 Skype Technologies, S.A. All rights reserved.
This Skype Security Bulletin may be reproduced and distributed,
provided that the Bulletin is not modified in any way and is
attributed to Skype Technologies, S.A. and provided that repro-
duction and distribution is performed for non-commercial purposes.
This Skype Security Bulltin is provided to you on an "AS IS" basis
and may contain information provided by third parties. Skype makes
no guarantees or warranties as to the information contained herein.
ANY AND ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT
LIMITATION WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE, OR NON-INFRINGEMENT, ARE HEREBY DISCLAIMED.
========================================================================
To report a security issue to Skype, please send an e-mail that
describes the problem or vulnerability to <security@skype.com>. Please
consider securing any reports that disclose security vulnerabilities by
encrypting them using the current PGP key of the Skype Computer
Emergency Response Team (SKY-CERT), PGP key ID 0xAD2DF320.
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