Rule:
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Sid:
659

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Summary:
This event is generated when a probe is sent to an SMTP server to determine if the decode alias is supported.

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Impact:
Intelligence gathering activity. This event could be an indication of reconnaissance or an actual attempt to overwrite a sensitive file. If the decode alias is present on the SMTP server, an attacker may use it to overwrite files. 

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Detailed Information:
The decode alias was included to allow email to be sent to a username of decode to process the email content through the uudecode program.  A malicious user could attempt to email a uuencoded file that would overwrite an existing sensitive file. 

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Affected Systems:
Older UNIX Sendmail versions (~1990-1996)

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Attack Scenarios:
An attacker can email a uuencoded file to the decode username to overwrite an existing sensitive file.  

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Ease of Attack:
Simple. Send email containing a uuencoded file to the username decode to overwrite an existing sensitive file.
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False Positives:
None Known.

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False Negatives:
None Known.

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Corrective Action:
Remove decode in /etc/aliases.

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Contributors:
Original rule written by Max Vision <vision@whitehats.com>
Sourcefire Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

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