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Inge Henriksen has discovered a weakness in Microsoft Office 2003, which can be exploited by malicious people to disclose sensitive information.

The weakness is caused due to Microsoft Office Outlook registering an unsafe "mailto" URI handler. This can be exploited to automatically attach an arbitrary file to an e-mail by tricking a user into following a specially crafted link with the "mailto:" URI handler from a malicious web site.

Example:
mailto:[mail]""..\..\..\..\..\[file]

The weakness has been confirmed on a fully patched system with Microsoft Office Outlook 2003 SP1/SP2 and Microsoft Office 2003 Professional Edition. Other versions may also be affected.

Solution
Validate attachments before sending e-mails after opening links with the "mailto:" URI handler.

Provided and/or discovered by
Inge Henriksen

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