CVE-2026-20171 MEDIUM

CVE-2026-20171: Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability

Vendor Cisco
Product Cisco NX-OS Software
Weakness CWE-670
Published May 20, 2026
Last update May 20, 2026

CVSS base score

6.8/10
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Confidentiality None
Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H

What the vulnerability does

01Description

A vulnerability in the Border Gateway Protocol (BGP) enforce-first-as feature of Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, remote attacker to trigger BGP peer flaps, resulting in a denial of service (DoS) condition. This vulnerability is due to incorrect parsing of a transitive BGP attribute. An attacker could exploit this vulnerability by sending a crafted BGP update through an established BGP peer session. If the update propagates to an affected device, it could cause the device to drop the BGP session and flap with the BGP peer that is forwarding this update, resulting in a DoS condition.

Key dates

02Disclosure timeline

May 20, 2026 CVE published
May 20, 2026 Record updated