271.txt

snort入侵检测规则文件2.4 Snort是众所周知的网络入侵检测工具

Rule:  
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Sid:
271

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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.

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

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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.

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Affected Systems:
 
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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).

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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 chargen service unless it is absolutely needed, and apply
ingress and egress filtering.

Additionally, disable the udp echo service.

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Contributors:
Original rule writer unknown
Snort documentation contributed by Jon Hart <[e-mail]>
Sourcefire Vulnerability Research Team
Nigel Houghton <[e-mail]>

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Additional References:



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