[NEWS] Yahoo! Mail Cross-Site Scripting Vulnerability

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  Yahoo! Mail Cross-Site Scripting Vulnerability
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SUMMARY

Finjan has discovered a script injection vulnerability in Yahoo! Mail that 
allows a remote attacker to execute malicious scripts when the victim is 
reading his/her mail.

DETAILS

Yahoo s mobile code filtering mechanism is based on an active content 
filter whose purpose is to block the injection of any active content into 
Yahoo! messages. Yahoo s filter identifies any instance of the inline use 
of the JavaScript protocol (e.g. JavaScript: ) and upon identification 
adds an underscore before the j , thus creating an invalid protocol 
request. The above filtering algorithm can be bypassed by inserting 
encoded tab characters (	) into the JavaScript string.

For example:
------------
< div style="background: url(j&#x0009;a&#x0009;v&#x0009;a&#x0009;
s&#x0009;c&#x0009;r&#x0009;i&#x0009;p&#x0009;t:alert());"></div>

Any tag that supports the style property can be used to call a JavaScript 
file. The injected JavaScript code could lead to:
 * Automatic launching of malicious code
 * Stealing the victim's password by using a spoofed re-login window
 * Reading the victim's INBOX and contacts
 * Sending an email message without any user authorization

Proof of Concept:
< div style="&#x000062;&#x000061;&#x00063;&#x00006B;&#x000067;&#x000072;
&#x00006F;&#x000075;&#x00006E;&#x000064;&#x00003A;&#x00075;&#x00072;
&#x0006C;&#x00028;j&#x00061;&#x0009;&#x0009;v&#x0009;&#x00061;&#x0009;
s&#x00063;&#x0009;&#x00072;&#x0009;&#x00069;&#x0009;&#x00070;&#x0009;
&#x00074;&#x0003A;alert());"></div>

Vulnerability Status:
Vendor was notified on Sep 8th, 2004. The bug is now fixed.


ADDITIONAL INFORMATION

The information has been provided by  <mailto:theinsider@012.net.il> Rafel 
Ivgi, The-Insider.



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