Cisco fixed CVE-2023-20049 DoS flaw affecting enterprise routers

March 12, 2023  By Pierluigi Paganini


Cisco fixed a high-severity DoS vulnerability (CVE-2023-20049) in IOS XR software that impacts several enterprise routers.

Cisco has released security updates to address a high-severity DoS vulnerability, tracked as CVE-2023-20049 (CVSS score of 8.6), in IOS XR software used by several enterprise-grade routers.

The vulnerability resides in the bidirectional forwarding detection (BFD) hardware offload feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers.

An unauthenticated, remote attacker can trigger the flaw to cause a line card to reset, resulting in a denial of service (DoS) condition.

An attacker can trigger the CVE-2023-20049 vulnerability by sending a crafted IPv4 BFD packet to a vulnerable device.

“This vulnerability is due to the incorrect handling of malformed BFD packets that are received on line cards where the BFD hardware offload feature is enabled.” reads the advisory published by the vendor. “. A successful exploit could allow the attacker to cause line card exceptions or a hard reset, resulting in loss of traffic over that line card while the line card reloads.”

This flaw affects Cisco routers running a vulnerable release of Cisco IOS XR 64-bit Software and have BFD hardware offload enabled for any of the installed line cards:

  • ASR 9000 Series Aggregation Services Routers only if they have a Lightspeed or Lightspeed-Plus-based line card installed
  • ASR 9902 Compact High-Performance Routers
  • ASR 9903 Compact High-Performance Routers

The company pointed out that this vulnerability does not affect the following Cisco products:

  • IOS Software
  • IOS XE Software
  • IOS XR Platforms not listed in the Vulnerable Products section of this advisory

As a workaround, Cisco recommends disabling the BFD hardware offload and creating Infrastructure Access Control lists.

The IT giant addressed the issue with the release of IOS XR versions 7.5.3, 7.6.2, and 7.7.1.

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Pierluigi Paganini

(SecurityAffairs – hacking, routers)



Pierluigi Paganini
Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.





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