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Yahoo/Hotmail scripting vulnerability, worm propagation
From: mparcens () hushmail com
Date: Wed, 30 May 2001 19:18:08 -0500 (EDT)

Title: Yahoo/Hotmail scripting vulnerability, worm propagation


Cross-site-scripting holes in Yahoo and Hotmail make it possible to replicate 
a Melissa-type worm through those webmail services.


An email is sent to the victim, who uses Yahoo Mail or Hotmail. Inside the 
email is a link to yahoo or hotmail's own server. The link contains escaped 
javascript that is executed when the page is loaded. That javascript then 
opens a window that could nagivate through the victim's inbox, sending messages 
with the malicious link to every email address it finds in the inbox. Because 
the malicious javascript executes inside a page from the mail service's 
own server, there is no domain-bounding error when the javascript is controlling 
the window with the victim's inbox.

Who is vulnerable

Users of the Yahoo Mail and Hotmail service. Although the exploit requires 
a user to click on a link, two things work for this exploit. (1) The email 
comes from a familiar user (sent by the worm), and (2) The link is to a 
familiar, trusted server. Theoretically, more services are vulnerable, due 
to the proliferation of these holes, but the worm is limited to web mail 


Sample links and the worm code can be found at: http://www.sidesport.com/webworm/


Escaping all query data that is echoed to the screen eliminates this problem. 
This must be done on every page on a server that can send or read mail for 
the service.

Vendor Status

Both Yahoo and Hotmail were notified on May 23 2001.

mparcens () hushmail com

Free, encrypted, secure Web-based email at www.hushmail.com

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