Rule:

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Sid:
1276

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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) ypserv is listening.

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

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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 ypserv run. The ypserv RPC service looks up information in the local Network Information Service (NIS) maps. The ypserv program provides the server function for Yellow Pages (YP) by providing clients information from NIS maps. Multiple vulnerabilities are associated with the ypserv RPC program.

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Affected Systems:
All hosts running the UNIX portmapper.

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

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Ease of Attack:
Simple.

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

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False Negatives:
This rule detects probes of the portmapper service for ypserv, not probes of the ypserv service itself. Because RPC services often listen on fairly arbitrary ports, it may not be possible to detect misuses of the ypserv service itself. An attacker may attempt to go directly to the ypserv 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 Vulnerability Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

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