Rule:

Sid:
578

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Summary:
This event is generated when an attempt is made through a portmap GETPORT request to discover the port where the Remote Procedure Call (RPC) cmsd is listening.

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Impact:
Information disclosure.  This request is used to discover which port cmsd is using.  Attackers can also learn what versions of the cmsd protocol are accepted by cmsd.

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Detailed Information:
The portmapper service registers all RPC services on UNIX hosts. It can be queried to determine the port where RPC services such as cmsd run.  The cmsd RPC service implements the Calendar Manager Service daemon that is often distributed with the Common Desktop Environment (CDE) and OpenWindows.  Several buffer overflow vulnerabilities have been associated with cmsd.

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Affected Systems:
Any host running the RPC service cmsd.

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Attack Scenarios:
An attacker can query the portmapper to discover the port where cmsd runs.  This may be a precursor to accessing cmsd.

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Ease of Attack:
Simple.  

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False Positives:
If a legitimate remote user is allowed to access cmsd, this rule may trigger.

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False Negatives:
This rule detects probes of the portmapper service for cmsd, not probes of the cmsd service itself. Because RPC services often listen on fairly arbitrary ports, it may not be possible to detect misuses of the cmsd service itself. An attacker may attempt to go directly to the cmsd port without querying the portmapper service, which would not trigger the rule.

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Corrective Action:
Limit remote access to RPC services.

Filter RPC ports at the firewall to ensure access is denied to RPC-enabled machines. 

Disable unneeded RPC services.

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Contributors:
Original rule written by Max Vision <vision@whitehats.com>
Modified by Brian Caswell <bmc@sourcefire.com>
Sourcefire Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

Arachnids 
http://www.whitehats.com/info/IDS17


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