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ipfw -- IP fragment denial of service


Problem description:

The firewall maintains a pointer to layer 4 header information in the event that it needs to send a TCP reset or ICMP error message to discard packets. Due to incorrect handling of IP fragments, this pointer fails to get initialized.


An attacker can cause the firewall to crash by sending ICMP IP fragments to or through firewalls which match any reset, reject or unreach actions.


Change any reset, reject or unreach actions to deny. It should be noted that this will result in packets being silently discarded.



portaudit: ipfw -- IP fragment denial of service

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If you have found a vulnerability in a FreeBSD port not listed in the database, please contact the FreeBSD Security Officer. Refer to "FreeBSD Security Information" for more information.

Oliver Eikemeier <>