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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
Overview
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.
Workaround
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 -
<http://www.cisco.com/warp/public/707/cisco-sa-20050126-les.shtml>
* Cisco Security Advisory: Multiple Crafted IPv6 Packets Cause
Reload -
<http://www.cisco.com/warp/public/707/cisco-sa-20050126-ipv6.shtml>
* Cisco Security Advisory: Cisco IOS Malformed BGP Packet Causes
Reload -
<http://www.cisco.com/warp/public/707/cisco-sa-20050126-bgp.shtml>
* US-CERT Vulnerability Note VU#583638 -
<http://www.kb.cert.org/vuls/id/583638>
* US-CERT Vulnerability Note VU#472582 -
<http://www.kb.cert.org/vuls/id/472582>
* US-CERT Vulnerability Note VU#689326 -
<http://www.kb.cert.org/vuls/id/689326>
_________________________________________________________________
Feedback can be directed to the authors: Will Dormann, Chad Dougherty,
and Damon Morda
_________________________________________________________________
This document is available from:
<http://www.us-cert.gov/cas/techalerts/TA05-026A.html>
_________________________________________________________________
Copyright 2005 Carnegie Mellon University.
Terms of use: <http://www.us-cert.gov/legal.html>
_________________________________________________________________
Revision History
January 26, 2005: Initial release
Last updated January 26, 2005
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