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Cisco IOS fails to properly handle malformed DHCP packets

Vulnerability Note VU#630104

Original Release Date: 2004-11-10 | Last Revised: 2004-11-11


A denial-of-service vulnerability exists in Cisco's Internetwork Operating System (IOS). This vulnerability may allow remote attackers to conduct denial-of-service attacks on an affected device.


The Dynamic Host Configuration Protocol (DHCP) provides a means for distributing configuration information to hosts on a TCP/IP network.The Cisco Internetwork Operating System (IOS) implementation of DHCP contains a vulnerability that allows malformed DHCP packets to cause an affected device to stop processing incoming network traffic.

Cisco devices place incoming DHCP packets into an input queue so that they can be processed. When an affected Cisco device encounters certain malformed DHCP packets that are undeliverable, it may allow these packets to remain in the queue. When the number of packets in the queue are equal to or greater than the size of the queue, the device will stop accepting traffic on that interface. Such packets can be sent by an unauthenticated remote attacker and may result in a denial-of-service condition.

By default, Cisco routers are configured to process DHCP packets. In order to regain functionality, the device must be rebooted to clear the input queue on the interface.


By sending a specially crafted DHCP packet to an affected device, a remote, unauthenticated attacker could cause the device to stop processing incoming network traffic. Repeated exploitation of this vulnerability could lead to a sustained denial-of-service condition. In order to regain functionality, the device must be rebooted to clear the input queue on the interface.


Apply a patch

Please refer to the "Software Versions and Fixes" section of the Cisco Security Advisory for more information on upgrading.


Cisco recommends a number of workarounds. For a complete list of workarounds, see the "Workarounds" section of the Cisco Security Advisory.

Vendor Information


Cisco Systems Inc. Affected

Updated:  November 10, 2004



Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


Please refer to Cisco Security Advisory "Cisco IOS DHCP Blocked Interface Denial-of-Service".

If you have feedback, comments, or additional information about this vulnerability, please send us email.

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This vulnerability was reported by the Cisco Systems Product Security Incident Response Team (PSIRT).

This document was written by Damon Morda.

Other Information

CVE IDs: None
Severity Metric: 55.13
Date Public: 2004-11-10
Date First Published: 2004-11-10
Date Last Updated: 2004-11-11 20:04 UTC
Document Revision: 16

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