Rule: 

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Sid: 603

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Summary: 
This event is generated when an attempt to modify access control permissions for remote shell logins is attempted.

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Impact: 
An attacker may have modified remote login permissions such that any host is allowed to initiate a remote session on the target host.

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Detailed Information: 
The rule generates an event when system reconfiguration is attempted via "rsh". 

The command "echo + +" is used to relax access control permissions for r-services to allow access from any site without the need for password authentication. 

This activity is indicative of attempts to abuse hosts using a default configuration. 

Some UNIX systems use the "rsh" service to allow a connection to the machine for establishing an interactive session.

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Attack Scenarios: 
An attacker finds a machine with "rsh" enabled and reconfigures it to allow access from any location

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

Use ssh for remote access instead of rlogin.

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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/IDS385

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