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Cisco IOS contains DoS vulnerability in MPLS packet processing

Vulnerability Note VU#583638

Original Release Date: 2005-01-26 | Last Revised: 2005-01-26


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


Multi Protocol Label Switching (MPLS) is designed to increase the speed of IP packet-forwarding by applying labels to packets. These labels are then used by MPLS enabled routers to make packet forwarding decisions. The Cisco Internetwork Operating System (IOS) implementation of MPLS contains a vulnerability that allows malformed MPLS packets to cause an affected device to reload. Such packets can be sent by an unauthenticated attacker on a local network segment connected to a vulnerable device interface and may result in a denial-of-service condition.

According to the Cisco advisory, this vulnerability affects devices that do not have MPLS Traffic Engineering globally enabled. If MPLS Traffic Engineering is disabled, devices that are configured with an interface that has MPLS disabled are vulnerable to attack via that interface only.

Cisco identified that the following products are affected:

    • 2600 and 2800 series routers
    • 3600, 3700 and 3800 series routers
    • 4500 and 4700 series routers
    • 5300, 5350 and 5400 series Access Servers


By sending a specially crafted MPLS packet to an affected device, an unauthenticated attacker on a local network segment connected to a vulnerable device interface could cause the device to reload. Repeated exploitation of this vulnerability could lead to a sustained denial-of-service condition.


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

Enable MPLS Traffic Engineering (MPLS TE)

Cisco strongly encourages that you upgrade to an unaffected version of the code. As a short term solution to mitigate against this vulnerability, Cisco recommends enabling MPLS Traffic Engineering (MPLS TE) globally. To apply this workaround, Cisco Express Forwarding (CEF) needs to be enabled on the device to enable MPLS TE.

CEF and MPLS TE can be enabled by the following commands.

Router(config)# ip cef
Router(config)# mpls traffic-eng tunnels

Having MPLS TE enabled will make the router immune to the attacks coming from any interface.

Vendor Information


Cisco Systems Inc. Affected

Updated:  January 26, 2005



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 "Crafted packet causes reload on Cisco routers".

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: 21.24
Date Public: 2005-01-26
Date First Published: 2005-01-26
Date Last Updated: 2005-01-26 19:14 UTC
Document Revision: 29

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