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 Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

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