Vulnerability Note VU#630104

Cisco IOS fails to properly handle malformed DHCP packets

Original Release date: 10 Nov 2004 | Last revised: 11 Nov 2004


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.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Cisco Systems Inc.Affected-10 Nov 2004
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



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: Unknown
  • Date Public: 10 Nov 2004
  • Date First Published: 10 Nov 2004
  • Date Last Updated: 11 Nov 2004
  • Severity Metric: 55.13
  • Document Revision: 15


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