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CERT Advisory CA-2002-16 Multiple Vulnerabilities in Yahoo! Messenger

   Original release date: June 05, 2002
   Last revised: --
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

     * Yahoo! Messenger version 5,0,0,1064 and prior for Microsoft
       Windows

Overview

   There are multiple vulnerabilities in Yahoo! Messenger. Attackers that
   are able to exploit these vulnerabilities may be able to execute
   arbitrary code with the privileges of the victim user. We have not
   seen active scanning for these vulnerabilities, nor have we received
   any reports of these vulnerabilities being exploited, but users should
   upgrade to version 5,0,0,1065 or later.

I. Description

   Yahoo! Messenger is a widely used program for communicating with other
   users over the Internet. On May 27, 2002, a buffer overflow and a URL
   validation vulnerability were discovered in the Yahoo! Messenger
   client for Microsoft Windows. Details of each vulnerability follow:

     VU#137115 - Yahoo! Messenger contains a buffer overflow in the URI
     handler

     The buffer overflow occurs during the processing of the Yahoo!
     Messenger URI handler (ymsgr:). This URI handler is installed at
     the system level for applications that use the underlying operating
     system when processesing URIs (such as Microsoft Internet Explorer,
     Netscape Navigator 6, Microsoft Outlook, or the command shell). A
     URI can be sent by another Yahoo! Messenger user in a message,
     embedded in a web site, or sent in an HTML-renderable email
     message.

     This vulnerability has been assigned as CAN-2002-0031 by the Common
     Vulnerabilities and Exposures (CVE) group:

     http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0031

     VU#172315 - Yahoo! Messenger "addview" function allows for the
     automatic execution of malicious script contained in web pages

     A vulnerability exists in the Yahoo! Messenger "addview" function
     that permits a remote attacker to execute arbitrary script and HTML
     in the Internet security zone of the local machine. The "addview"
     function is only supposed to accept view information from Yahoo!
     servers. However, an attacker can send malicious script and HTML to
     the client using the Yahoo! URL redirection service. This script or
     HTML is interpreted by the Yahoo! Messenger client and is displayed
     in the client's web browser.

     This vulnerability has been assigned as CAN-2002-0032 by the Common
     Vulnerabilities and Exposures (CVE) group:

     http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0032

   These vulnerabilities were resolved in Yahoo! Messenger version
   5,0,0,1065, released May 22, 2002; however, a bug in the distribution
   server may have inadvertantly installed Yahoo! Messenger version
   5,0,0,1036 on systems that downloaded Yahoo! Messenger after May 22,
   2002. The bug in the distribution server has since been resolved.

   In February 2002, the following vulnerabilities were reported to
   affect Yahoo! Messenger:

     * http://www.kb.cert.org/vuls/id/393195
     * http://www.kb.cert.org/vuls/id/419419
     * http://www.kb.cert.org/vuls/id/755755
     * http://www.kb.cert.org/vuls/id/887319
     * http://www.kb.cert.org/vuls/id/952875

   All of these vulnerabilities were resolved in Yahoo! Messenger version
   5,0,0,1058, released February 25, 2002, or by server-side resolutions
   around the same time.

II. Impact

   A remote attacker can execute arbitrary code with the privileges of
   the victim user, cause a denial of service, or modify data in the
   victim's buddy list.

III. Solution

   Upgrade to the latest version of Yahoo! Messenger

     On May 22, 2002, Yahoo! released a fixed version of Yahoo!
     Messenger (5,0,0,1065) and began issuing a patch (5,0,0,1066) via
     the AutoUpdater to address this issue. All users should upgrade to
     version 5,0,0,1065 or later. Users with versions prior to
     5,0,0,1066 that have "Auto Update" enabled will receive a message
     informing them that an upgrade is available. All users should
     accept this upgrade.

     Users who downloaded Yahoo! Messenger after May 22, 2002, should be
     aware that a bug in the distribution server may have inadvertantly
     installed Yahoo! Messenger version 5,0,0,1036, which is vulnerable
     to all issues in this advisory. The bug in the distribution server
     has since been resolved.

     Users should upgrade and verify the version of Yahoo! Messenger by
     selecting the "About Yahoo! Messenger..." option from the Help
     menu.

   Implement a firewall and filtering

     Yahoo! Messenger listens for peer-to-peer requests on port 5101/TCP
     but users can implement a firewall to block inbound and outbound
     access to port 5101/TCP. However, since Yahoo! Messenger URI's can
     be embedded in a web site or email message, blocking requests to
     and from port 5101/TCP is not a completely effective solution. Mail
     and Internet filters should also be applied to filter the "ymsgr:"
     URI handler from email messages and web sites.

Appendix A. - Vendor Information

   This appendix contains information provided by vendors for this
   advisory. When vendors report new information to the CERT/CC, we
   update this section and note the changes in our revision history. If a
   particular vendor is not listed below, we have not received their
   comments.

Yahoo!, Inc.

     Yahoo! encourages users to upgrade to the latest version whenever
     prompted by the AutoUpdater or regularly check for updated versions
     of the client at http://messenger.yahoo.com.
     _________________________________________________________________

   The CERT Coordination Center thanks Scott Woodward
   <scottphoenixtechie.com>, Phuong Nguyen <dphuongyahoo.com>, and Adam
   Lang <themeetuphotmail.com> for their discovery and analysis of these
   vulnerabilities. We also thank Yahoo! for their assistance in
   analyzing and responding to these issues.
     _________________________________________________________________

   Feedback can be directed to the author: Jason A. Rafail
     _________________________________________________________________

Appendix B. - References

    1. http://www.kb.cert.org/vuls/id/137115
    2. http://www.kb.cert.org/vuls/id/172315
    3. http://www.kb.cert.org/vuls/id/393195
    4. http://www.kb.cert.org/vuls/id/419419
    5. http://www.kb.cert.org/vuls/id/755755
    6. http://www.kb.cert.org/vuls/id/887319
    7. http://www.kb.cert.org/vuls/id/952875
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2002-16.html
   ______________________________________________________________________

CERT/CC Contact Information

   Email: certcert.org
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   Revision History
      June 05, 2002: Initial release

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