Rule:

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Sid: 527

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Summary:
This event is generated when traffic on the network is using the same 
source and destination IP address.

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Impact:
Possible Denial of Service.

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Detailed Information:
Under normal circumstances traffic to and from the same IP address 
should not be seen on the network. This may be an indicator for the Land
attack tool.

Some TCP/IP stacks hang or even crash when presented with a TCP SYN 
packet containing the same source and destination IP address. Some 
target hosts will crash others will be temporarily disabled.

an indicator of unauthorized network use, reconnaisance activity or 
system compromise. These rules may also generate an event due to 
improperly configured network devices.

A packet that has the same source and destination IP addresses directed to TCP
port 7007 or 7778 can cause a denial of service for Windows Media Station or
Windows Media Monitor on Windows 2000 hosts SP2, SP3, SP4 running Windows Media
services 4.0 or 4.1 will also generate an event from this rule.

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Affected Systems:
	Multiple systems from multiple vendors.

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Attack Scenarios:
The attacker may send traffic from a spoofed source address, in this 
case the victims IP address.

The attacker may be using the Land attack tool.

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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:
Employ egress filtering at the border router or firewall.

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Contributors:
Original rule writer unknown
Sourcefire Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

SANS:
http://www.sans.org/rr/firewall/egress.php

CERT:
http://www.cert.org/advisories/CA-1997-28.html

Bugtraq:
http://www.securityfocus.com/bid/9825

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