Yahoo! Messenger is an instant messaging client. When installed, Yahoo! Messenger enables a URI handler (ymsgr :parameter). The addview function of this handler can be used to execute arbitrary script/html on the local system.
The addview feature of Yahoo! Messenger is used to allow users to view content from a site that is formatted in the Yahoo! Messenger format without the need for a stand-alone web browser. If the attacker can trick the user into visiting a website or opening an HTML-renderable email, the attacker can exploit this vulnerability to execute arbitrary script/HTML on the local system with the privileges of the current user.
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. The arbitrary script/HTML is executed on the local system in the Internet security zone.
This vulnerability was reported on by Phuong Nguyen of Vice Consulting.