File: 271.txt

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Rule:  
--
Sid:
271

--
Summary:
This event is generated when an attempt is made to issue a Denial of
Service attack against a host or network by generating traffic between 
your udp echo port and their udp chargen port.

--
Impact:
Potential Denial of service (DoS) condition for the target host, hosts
between the target host and the attacker, and more.

--
Detailed Information:
Traffic was detected between the udp echo port on a host on the
protected network and the udp chargen (character generator) service.  
Due to the connectionless nature of udp, a single packet from the udp chargen
service to a listening udp echo service will result in mass quantities
of traffic back and forth between the two services.

--
Affected Systems:
 
--
Attack Scenarios:
An attacker will find a host that still provides the udp chargen service
and generate traffic between it and the udp echo service on a machine.
If proper ingress/egress filtering is not in place, this traffic can be 
trivially spoofed provided the attacker has elevated privledges on the 
attacking/initiating machine (the source port being less than 1024).

--
Ease of Attack:
Simple.

--
False Positives:
None Known

--
False Negatives:
None Known

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Corrective Action:
Disable the chargen service unless it is absolutely needed, and apply
ingress and egress filtering.

Additionally, disable the udp echo service.

--
Contributors:
Original rule writer unknown
Snort documentation contributed by Jon Hart <warchild@spoofed.org>
Sourcefire Vulnerability Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>

-- 
Additional References:



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