I. BACKGROUND Yahoo! Messenger is a instant messaging application that allows users to chat online, share files, conduct PC to PC calls and more. More information can be found on the vendor's site at the following URL. http://messenger.yahoo.com/ II. DESCRIPTION Remote exploitation of multiple buffer overflow vulnerabilities in Yahoo Inc.'s Yahoo! Messenger 8.1 allows attackers to execute arbitrary code with the privileges of the currently logged in user. When Yahoo Messenger 8.1 is installed, the following vulnerable ActiveX Control is registered on the system. ProgID: YVerInfo.GetInfo.1 Clsid: D5184A39-CBDF-4A4F-AC1A-7A45A852C883 File: C:\Program Files\Yahoo!\Common\YVerInfo.dll Version: 2006.8.24.1 Stack based buffer overflows can be triggered through either the fvCom() or info() methods of this class. III. ANALYSIS Exploitation allows attackers to execute arbitrary code with the privileges of the currently logged in user. Users would be required to have a vulnerable version of the target software installed and be lured to a malicious site. It is important to note that functions within this class can only be called if the control believes it is being run from the yahoo.com domain. In order for this exploit to be triggered an attacker would either have to leverage a Cross-Site Scripting vulnerability in the yahoo.com domain, or be able to control the targeted user's DNS resolution for the domain. IV. DETECTION iDefense has confirmed the existence of this vulnerability in version 8.1 of Yahoo Instant Messenger. Previous versions are suspected to be vulnerable as well. V. WORKAROUND Setting the kill bit for the vulnerable ActiveX control's CLSID will prevent these issues from be exploited within Internet Explorer. VI. VENDOR RESPONSE Yahoo Inc. has addressed these vulnerabilities by releasing an updated version of Yahoo! Messenger. More information is available at the following URL. http://messenger.yahoo.com/security_update.php?id=082907 VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-4515 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 08/21/2007 Initial vendor notification 08/21/2007 Initial vendor response 08/30/2007 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2007 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customer service for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.