Rule:

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Sid:
501

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Summary:
This event is generated when a packet is discovered with loose source routing set in the IP options.

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Impact:
Loose source routing permits the dictation of a route to and from the destination rather than relying on standard dynamic routing.

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Detailed Information:
Loose source routing instructs the packet to traverse identified routers in transit to and from the desired destination.  Normal routing sends a packet one hop at a time allowing each interim router to determine the next hop.  This may permit an attacker to spoof a source IP yet receive the response by sniffing from a network associated with an identified loose source router.  A vulnerability exist in Windows 95, 98, and NT hosts that permits a vulernable destination host to accept a specially crafted source routed packet even though the host has a registry setting to drop it.

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Affected Systems:
Unless loose source routing is disabled, all hosts can accept them.

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Attack Scenarios:
An attacker can craft a special source routed packet to cause Windows 95, 98, and NT hosts to accept them even though a registry setting exists to drop source routed packets.

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Ease of Attack:
Simple.  

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False Positives:
This even will trigger if you allow loose source routed packets into your network.

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False Negatives:
None Known.

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Corrective Action:
Block all source routed (loose or strict) packets from entering your network.

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Contributors:
Original rule written by Max Vision <vision@whitehats.com>
Modified by Brian Caswell <bmc@sourcefire.com>
Sourcefire Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

CVE
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-1999-0909

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