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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
* 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.
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.
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.
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 - <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> ___________
January 26, 2005: Initial release
Last updated January 26, 2005
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