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CA-2002-16 Multiple Vulnerabilities in Yahoo! Messenger


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


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

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

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

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:

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:


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

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

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

The CERT Coordination Center thanks Scott Woodward
<>, Phuong Nguyen <>, and Adam
Lang <> 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


This document is available from:

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Revision History
June 05, 2002: Initial release

Version: PGP 6.5.8


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