Rule: 

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Sid: 610

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Summary: 
This event is generated when an attempt to login as the superuser is attempted using rsh.

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Impact: 
Serious. If successful the attacker may have gained superuser access to the host.

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Detailed Information: 
This rule generates an event when a connection is made using "rsh" with the username "root". Such activity is indicative of attempts to abuse insecure machines with a known default configuration. 

Some UNIX systems use the "rsh" daemon which permits remote "root" logins. This may allow an attacker to connect to the machine and establish an interactive session.

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Attack Scenarios: 
An attacker finds a machine with the "rsh" service running and connects to it, then proceeds to guess the "root" password

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Ease of Attack:
Simple, no exploit software required

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False Positives: 
A system administrator may be logging in to a host using the username "root"

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False Negatives: 
If a local username is not the same as the remote one ("root"), the rule will not generate an event.

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Corrective Action: 
Investigate logs on the target host for further details and more signs of suspicious activity

Use ssh for remote access instead of rsh.

Deny remote root logins to the host, use a normal user and "sudo" or give the user the ability to "su" to root where appropriate.

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Contributors:
Original rule by Max Vision <vision@whitehats.com> modified from a signature written by Ron Gula
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/IDS391

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