Rule:

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Sid:
1251

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Summary:
This event is generated when an unsuccessful telnet login attempt 
was detected.

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Impact:
Serious. Possible unauthorized access.

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Detailed Information:
A user tried to log on to a system via telnet, but has been rejected, 
either due to invalid username, password, or both. This could mean 
someone is trying to log on without a proper password (if there are 
multiple unsuccessful logins) or they may have just mistyped the 
username or the password.

A large number of these events may indicate an attempt to access the 
system using a brute force method of guessing usernames and passwords.

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Affected Systems:
Machines running telnet servers.

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Attack Scenarios:
Attacker brute-forces passwords for a known username via a script or 
application.

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Ease of Attack:
Simple.

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False Positives:
A user may have mistyped their password.

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False Negatives:
None known.

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Corrective Action:
Check how many invalid attempts occurred, change the password of the 
user that tried to log in.

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Contributors:
Original Rule Writer Unknown
Snort documentation contributed by Chaos <c@aufbix.org>
Sourcefire Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

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