CVE-2026-20171CWE-670

Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability

Medium · published May 20, 2026

CVSS v3.1
6.8
EPSS
0%
Percentile
39.4
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
6.8 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00467 · 39.4th percentile
Weakness
CWE-670 · Always-Incorrect Control Flow Implementation
Published
2026-05-20T16:06Z
EPSS history
Timeline
  • 20 MAY 16:06Z
    Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
    cvelistv5