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# $Id: 796.txt,v 1.1 2002/04/04 02:07:54 cazz Exp $
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Rule:  

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Sid:
796

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Summary:
Using two or more windows file extensions, mail users have
difficulties to determine the type of attachments an probably
execute a file or script while thinking it is a harmless Excel
spreadsheet.

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Impact:
Mail worms may spread rapidly because users execute them.

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Detailed Information:
Windows systems are often configured not to display file extensions.
By adding a second extension, users get confused and think that an
executable is an EXCEL spreadsheet - e.g. businnesplan.xls.vbs gets displayed as
businessplan.xls but is a visual basic script and not an EXCEL spreadsheet.

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Attack Scenarios:
Famous worms (ILOVEYOU, KOURNIKOVA) are based on this method. Warning:
An EXCEL spreadsheet is in now way more secure than a visual basic script.
Wrongly configured antivirus software my ignore this files and
let a macro virus pass.

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Ease of Attack:
Very easy. One needs to attach a file and hope that it gets executed.

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False Positives:
Could be an error on sender's side.

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False Negatives:
-

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Corrective Action:
Use antivirus software. Configure mail clients securely, especially when
using windows desktops. Educate your mail users. Deny all attachments at
the gateway if you can.

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Contributors:
tobias.haecker@to.com

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Additional References:
See websites of antivirus companies.
