[NEWS] Yahoo! Mail Cross-Site Scripting Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 12/20/04

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Date: 20 Dec 2004 18:29:52 +0200

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      Yahoo! Mail Cross-Site Scripting Vulnerability
    ------------------------------------------------------------------------

    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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