Rule:

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Sid:
473

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Summary:
This event is generated when an ICMP Redirect Network message was
detected in network traffic.

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Impact:
Unknown. Possible system crash, Denial of Service (DoS) for some
embedded operating systems.

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Detailed Information:
Several susceptible IP Stack implementations may result in the system
hanging or crashing when malformed or corrupted ICMP Redirect Network
(Type 5, Code 0) packets are sent to them.  This vulnerability was first
discovered in 1997.

Under normal network conditions ICMP Redirect Network packets will occur
in a number of situations. One such situation is when a host is on a
subnet with more than one router. The host can only have one default
gateway, and forwards all traffic for networks outside its own subnet to
this gateway. If the default gateway detects that the gateway for this
route is on the same subnet as the originating host, the default gateway
forwards the packet onto this gateway and sends an ICMP Redirect Network
to the originating host.

This funtionality exists primarily to save network administrators from
having to keep extensive routing tables on hosts, the host will remember
the route learned from the ICMP Redirect Network message for a period of
time, and will forward any traffic directly while it has the route in
its cache.

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Affected Systems:
	All systems

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Attack Scenarios:
A malicious user may send corrupted ICMP Redirect Net messages to
networks in an attempt to crash a system.

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Ease of Attack:
Simple.

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False Positives:
Any ICMP Network Redirect will generate an event.

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False Negatives:
None Known

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Corrective Action:
Patches for Microsoft Windows NT 4.0 were included in SP4, and also
release as a post SP3 fix - teardrop2-fix.  Fixes are also available for
Windows 95 and various embedded systems.

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Contributors:
Original rule writer unknown
Original document author unkown
Sourcefire Vulnerability Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

Microsoft KB, Q154174
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