Rule:

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Sid:
2031

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Summary:
The rpc.ypasswd service is used to update user information remotely. 
This service should not be available outside the local area network, 
external source.

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Impact:
This may be an intelligence gathering activity on available rpc services
on a machine connected to external resources. The possibility also 
exists that an attacker may already have gained access to a NIS server 
and thus all resources connected to that host.

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Detailed Information:
A vulnerability exists in some versions of the rpc.ypasswd service that
can lead to a remote root compromise of a vulnerable host. This activity
may be an intelligence gathering exercise to ascertain wether or not the
host is vulnerable to this attack.

This activity may also indicate a possible compromise of a NIS server 
via a legitimate user account the attacker has previously garnered. 
Compromise of a master NIS server may present the attacker with easy 
access to all NIS resources the machine is connected to.

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Affected Systems:
All systems running the rpc.ypasswd service.

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Attack Scenarios:
The attacker can make a request to update user information via 
rpc.ypasswd.

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Ease of Attack:
Simple

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False Positives:
None Known

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False Negatives:
None Known

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Corrective Action:
Disable the rpc.ypasswd daemon.

Disallow all RPC requests from external sources and use a firewall to 
block access to RPC ports from outside the LAN.

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

SANS:
http://www.sans.org/rr/unix/NIS.php
http://www.sans.org/rr/unix/sec_solaris.php

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