US-CERT Technical Cyber Security Alert TA05-026A -- Multiple Denial-of-Service Vulnerabilities in Cisco IOS

Type securityvulns
Reporter Securityvulns
Modified 2005-01-27T00:00:00



            Technical Cyber Security Alert TA05-026A
    Multiple Denial-of-Service Vulnerabilities in Cisco IOS

Original release date: January 26, 2005 Last revised: -- Source: US-CERT

Systems Affected

 * Cisco routers and switches running IOS in various configurations


Several denial-of-service vulnerabilities have been discovered in Cisco's Internet Operating System (IOS). A remote attacker may be able to cause an affected device to reload the operating system.

I. Description

Cisco has published three advisories describing flaws in IOS that could allow a remote attacker to cause an affected device to reload. Further details are available in the following vulnerability notes:

VU#583638 - Cisco IOS contains DoS vulnerability in MPLS packet processing

The IOS implementation of Multi Protocol Label Switching (MPLS) contains a vulnerability that allows malformed MPLS packets to cause an affected device to reload. An unauthenticated attacker can send these malformed packets on a local network segment that is connected to a vulnerable device interface.

VU#472582 - Cisco IOS IPv6 denial-of-service vulnerability

A vulnerability in the way that IOS handles a sequence of specially crafted IPv6 packets could cause an affected device to reload, resulting in a denial of service. The vulnerability is exposed on both physical interfaces (i.e., hardware interfaces), and logical interfaces (i.e., software defined interfaces such as tunnels) that are configured for IPv6.

VU#689326 - Cisco IOS vulnerable to DoS via malformed BGP packet

An IOS device that is enabled for Border Gateway Protocol (BGP) and set up with the bgp log-neighbor-changes option is vulnerable to a denial-of-service attack via a malformed BGP packet.

II. Impact

Although the underlying causes of these three vulnerabilities is different, in each case a remote attacker could cause an affected device to reload the operating system. This creates a denial-of-service condition since packets are not forwarded through the affected device while it is reloading. Repeated exploitation of these vulnerabilites would result in a sustained denial-of-service condition.

Since devices running IOS may transit traffic for a number of other networks, the secondary impacts of a denial of service may be severe.

III. Solution

Upgrade to a fixed version of IOS

Cisco has updated versions of its IOS software to address these vulnerabilities. Please refer to the "Software Versions and Fixes" sections of the Cisco Security Advisories listed in Appendix A for more information on upgrading.


Cisco has also published practical workarounds for VU#689326 and VU#583638. Please refer to the "Workarounds" section of each Cisco Security Advisory listed in Appendix A for more information.

Sites that are unable to install an upgraded version of IOS are encouraged to implement these workarounds.

Appendix A. References

 * Cisco Security Advisory: Crafted Packet Causes Reload on Cisco
   Routers -
 * Cisco Security Advisory: Multiple Crafted IPv6 Packets Cause
   Reload -
 * Cisco Security Advisory: Cisco IOS Malformed BGP Packet Causes
   Reload -
 * US-CERT Vulnerability Note VU#583638 -
 * US-CERT Vulnerability Note VU#472582 -
 * US-CERT Vulnerability Note VU#689326 -

Feedback can be directed to the authors: Will Dormann, Chad Dougherty, and Damon Morda ___________

This document is available from: <> ___________

Copyright 2005 Carnegie Mellon University. Terms of use: <> ___________

Revision History

January 26, 2005: Initial release

                   Last updated January 26, 2005

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