Title: Yahoo/Hotmail scripting vulnerability, worm propagation Synopsis Cross-site-scripting holes in Yahoo and Hotmail make it possible to replicate a Melissa-type worm through those webmail services. Description 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 services. Proof-of-Concept Sample links and the worm code can be found at: http://www.sidesport.com/webworm/ Solution 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 mparcensat_private Free, encrypted, secure Web-based email at www.hushmail.com IMPORTANT NOTICE: If you are not using HushMail, this message could have been read easily by the many people who have access to your open personal email messages. Get your FREE, totally secure email address at http://www.hushmail.com.
This archive was generated by hypermail 2b30 : Thu May 31 2001 - 08:43:07 PDT