Vulnerability Note VU#630104

Cisco IOS fails to properly handle malformed DHCP packets

Overview

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.

I. Description

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.

II. Impact

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.

III. Solution

Apply a patch

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

Workarounds

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

Systems Affected

Vendor	Status	Date Notified	Date Updated
Cisco Systems Inc.	Vulnerable	10-Nov-2004

References

http://www.cisco.com/warp/public/707/cisco-sa-20041110-dhcp.shtml
http://www.ietf.org/rfc/rfc2131.txt

Credit

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

This document was written by Damon Morda.

Other Information

Date Public:	2004-11-10
Date First Published:	2004-11-10
Date Last Updated:	2004-11-11
CERT Advisory:
CVE-ID(s):
NVD-ID(s):
US-CERT Technical Alerts:
Metric:	55.13
Document Revision:	15

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