Rule:   

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Sid: 322

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Summary: 
This event is genrated when an attempt is made to query the finger daemon to ascertain a list of usernames on a system.

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Impact: 
Information gatthering, the attacker may obtain the list of some accounts existing on the victim system as a prelude to further compromize.

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Detailed Information:

The rule is triggerred when an attempt to use a search feature in
"cfingerd" version of a finger daemon is attempted. The search feature
allows the attacker to obtain the lists of accounts existing on the
target system by issuing a specially crafted finger request to
"search" for information. Knowing the list of accounts might
facilitate a password guessing attacks, email attacks or other abuse.

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Attack Scenarios: an attacker learns that "guest" account exists and
has never been used. He then guesses that the password for this
account and logs in to the system remotely using telnet.

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Ease of Attack: 
Simple, no exploit software required

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False Positives:
None Known

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False Negatives: 
None Known

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Corrective Action: 
Look for other IDS events involving the same IP addresses. 

Look for suspicious logins to the affected system.

Disable the finger daemon or apply a vendor patch that removes the vulnerability

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Contributors: 
Original rule writer Max Vision <vision@whitehats.com>
Snort documentation contributed by Anton Chuvakin <http://www.chuvakin.org>
Sourcefire Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

Arachnids:
http://www.whitehats.com/info/IDS375

CVE:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-1999-0259

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