-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 ________________________________________________________________________ SKYPE SECURITY BULLETIN SKY-CERT Bulletin title: Improper handling of URI arguments Bulletin ID: SKYPE-SB/2006-002 Bulletin status: FINAL Date of announcement: 2006-10-03 15:00:00 +0000 Products affected: Skype for Mac Vulnerability type: Argument handling CVE references: CVE-2006-5084 Risk assessment: HIGH CVSS base score: 10.0 (AV:R/AC:L/Au:NR/C:C/I:C/A:C/B:N) Cross-references: http://www.securityfocus.com/bid/20218 http://securitytracker.com/id?1016966 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 ----------- A security bug in the Skype for Mac user client has been identified and fixed. In some circumstances, a Skype URL can be crafted that, if followed, could cause the execution of arbitrary code on the platform on which Skype is running. Discussion ---------- An attacker who constructs a Skype URL that is malformed in a specific way can cause Skype to crash or, in some cases, allow for the execution of arbitrary instructions. For the vulnerability to be triggered, the target must follow a malformed Skype URL. This behavior is due to incorrect handling of arguments passed to a function in the Skype URI handler that initializes an alert panel. In some cases the function prototype is not respected, allowing for the format parameter to be filled from the URI string itself instead of being of a fixed format. This, in turn, can allow the kinds of format string vulnerabilities outlined in the following document: https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/ guidelines/340.html The attack requires the targeted user to manually follow a specially crafted malformed link, such as on a web page. Depending on several factors, doing so may result in an application crash, possibly succeeded by the execution of arbitrary code. This is tracked by Mitre CVE ID CVE-2006-5084. ________________________________________________________________________ 2. Impact and affected software Impact ------ A user of Skype for Mac who follows a specially-crafted URL may experience a crash of the Skype software and possibly may execute arbitrary code without consent. Affected Software ----------------- The following Skype clients are vulnerable to this attack: Skype for Mac: All releases prior to and including 1.5.*.79 ________________________________________________________________________ 3. Solution or work-around An official fix to the issue covered by this Security Bulletin has been released. To implement this fix, update to one of the following releases of Skype. (Downloading instructions are shown in Section 5 of this Bulletin.) Skype for Mac: Skype 1.5, release 1.5.*.80 or later ________________________________________________________________________ 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 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: Access Vector (AV) ........... Remote Access Complexity (AC) ....... Low Authentication (Au) .....,.... Not Required Confidentiality Impact (C) ... Complete Integrity Impact (I) ......... Complete Availability Impact (A) ...... Complete Impact Bias (B) .............. Normal Computed CVSS base score: 10.0 Temporal metrics as of 2006-10-03 Exploitability (E) ........... Functional Remediation Level (RL) ....... Official Fix Report Confidence (RC) ....... Confirmed Computed CVSS temporal score: 8.3 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 Tom Ferris of Security- Protocols.com for having referred this problem to Skype. ________________________________________________________________________ 9. Bulletin release history 2006-10-03 Initial bulletin release ________________________________________________________________________ 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 . 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. ======================================================================== -----BEGIN PGP SIGNATURE----- Version: PGP Desktop 9.0.6 (Build 6060) iQEVAwUBRSJwVk5QOg6tLfMgAQhOPggAkzD7OYlM+fhG6itXKF6SSoRt7VcGkxsg ggwTM+T2bwTHpbRgTQDv7kuECeuagRnUX/iklNbg3bITMJ3BRp/w2480uerqRF8o XmR5DAbQt1ISoofblYIJfA/94EYJYU8kQL2MYsh6tz1dCwzxWuATX5FSkrwh0VIY wvsf5vy4BTSgzulLXbNy/GGqPu/OLZOSYwMijwq0jJdVqPw2+R+OU4sp5609VwNK 9sJ/nVxylMOSRZdRIa3fCh8pIvcN23/f26eU7FuCTlh4cX9D4HlPOtIqZLo6WcJy 3TPJGByfPIJwUvfZhP5drNVSYf7vunoOfv5iVx1x7+Jx37McL9WJbQ== =aRUb -----END PGP SIGNATURE-----