Rule:
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Sid:
269

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Summary:
A denial of service attack known as Land has been launched. Some TCP/IP 
stacks crash or hang when sent a spoofed TCP SYN packet with the same 
source and destination host and the same source and destination port.  

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Impact:
Denial of service against a target host.

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Detailed Information:
The Land denial of service attack attempts to crash or disable a target 
host by sending a spoofed TCP SYN packet with an identical source and 
destination IP and identical source and destination port.  Some target 
hosts will crash others will be temporarily disabled.  

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Affected Systems:
	Windows 95
	Windows NT Any unpatched version 
	SCO CMW+ 3.0
	SCO Open Desktop/Open Server 3.0
	SCO Open Server 5.0
	SCO UnixWare 2.1.0
	Gauntlet 3.2/HP-UX 10.10 and Gauntlet 4.1/HP-UX 10.20

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Attack Scenarios:
A malicious user crafts a packet to cause a Denial of Service against a 
target host.

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Ease of Attack:
Simple to craft such a packet using any number of packet crafting tools 
such as nmap and hping.


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False Positives:
None known.  This should have a very low likelihood of false positives.

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False Negatives:
The exploit code has an IP identification number and TCP sequence number
of 3868.  If a user changes the source code to have a different IP 
identification or TCP sequence number, the rule will not fire. 

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Corrective Action:
Malicious outside attacks can be prevented by configuring your 
packet-filtering device to block packets from entering your network that
have source IP's from your network address space. 

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

CVE:
CAN-1999-0016

CERT:
CA-1997-28

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