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By | John Leyden 12th June 2006 15:28

JavaScript worm targets Yahoo!

Malware latches onto unpatched flaw

A JavaScript worm that takes advantage of an unpatched vulnerability in Yahoo!'s webmail service has been discovered on the net.

The JS-Yamanner worm spreads when a Windows user accesses Yahoo! Mail to open an email sent by the worm. The attack works because of a vulnerability in Yahoo! Mail that enables scripts embedded within HTML emails to be run within a user’s browser instead of being blocked.

Once executed, the worm forwards itself to an infected users' contacts on Yahoo! Mail. It also harvests these address and sends them to a remote internet server. Only contacts with an email address of either or are hit by this behaviour.

Infected emails commonly have the subject line "New Graphic Site" and are spoofed so as to appear from "". Users who open infected emails will be redirected to a webpage at

Symantec Security Response senior manager Kevin Hogan said: "Unlike its predecessors, which would require the user to open an attachment in order to launch and propagate, JS-Yamanner makes use of a security hole in the Yahoo! web mail program in order to spread to other Yahoo! users. Yahoo! is a popular email tool, and although normally closed to such threats, the exploitation of this vulnerability provides access to a significant number of internet users.

"As there is no patch at present, users are recommended to update virus definitions and firewall signatures and to block any emails sent from" ®

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