CVE-2026-20171
Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
Description
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.
INFO
Published Date :
May 20, 2026, 5:16 p.m.
Last Modified :
July 23, 2026, 12:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Apply Cisco Nexus software updates.
- Configure BGP to mitigate attribute parsing issues.
- Monitor BGP peer session stability.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-20171.
| URL | Resource |
|---|---|
| https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-iefab-3hb2pwtx |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-20171 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-20171
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-20171 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-20171 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Jul. 23, 2026
Action Type Old Value New Value Added Translation Title: Cisco NX-OS Software, Description: Una vulnerabilidad en la característica enforce-first-as del Border Gateway Protocol (BGP) de los switches Cisco Nexus de la serie 3000 y los switches Cisco Nexus de la serie 9000 en modo NX-OS autónomo podría permitir a un atacante remoto no autenticado activar caídas de pares BGP, lo que resultaría en una condición de denegación de servicio (DoS). Esta vulnerabilidad se debe a un análisis incorrecto de un atributo BGP transitorio. Un atacante podría explotar esta vulnerabilidad enviando una actualización BGP manipulada a través de una sesión de par BGP establecida. Si la actualización se propaga a un dispositivo afectado, podría hacer que el dispositivo caiga la sesión BGP y tenga un flap con el par BGP que está reenviando esta actualización, lo que resultaría en una condición de DoS. -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'Cisco', 'product': 'Cisco NX-OS Software', 'versions': [{'status': 'affected', 'version': '10.2(1)'}, {'status': 'affected', 'version': '10.2(1q)'}, {'status': 'affected', 'version': '10.2(2)'}, {'status': 'affected', 'version': '10.2(3)'}, {'status': 'affected', 'version': '10.2(3t)'}, {'status': 'affected', 'version': '10.2(2a)'}, {'status': 'affected', 'version': '10.3(1)'}, {'status': 'affected', 'version': '10.2(4)'}, {'status': 'affected', 'version': '10.3(2)'}, {'status': 'affected', 'version': '10.3(3)'}, {'status': 'affected', 'version': '10.2(5)'}, {'status': 'affected', 'version': '10.2(3v)'}, {'status': 'affected', 'version': '10.4(1)'}, {'status': 'affected', 'version': '10.3(99w)'}, {'status': 'affected', 'version': '10.2(6)'}, {'status': 'affected', 'version': '10.3(3w)'}, {'status': 'affected', 'version': '10.3(99x)'}, {'status': 'affected', 'version': '10.3(3o)'}, {'status': 'affected', 'version': '10.3(4)'}, {'status': 'affected', 'version': '10.3(3p)'}, {'status': 'affected', 'version': '10.3(4a)'}, {'status': 'affected', 'version': '10.4(2)'}, {'status': 'affected', 'version': '10.3(3q)'}, {'status': 'affected', 'version': '10.3(5)'}, {'status': 'affected', 'version': '10.2(7)'}, {'status': 'affected', 'version': '10.4(3)'}, {'status': 'affected', 'version': '10.3(3x)'}, {'status': 'affected', 'version': '10.3(4g)'}, {'status': 'affected', 'version': '10.5(1)'}, {'status': 'affected', 'version': '10.2(8)'}, {'status': 'affected', 'version': '10.3(3r)'}, {'status': 'affected', 'version': '10.3(6)'}, {'status': 'affected', 'version': '10.4(4)'}, {'status': 'affected', 'version': '10.3(4h)'}, {'status': 'affected', 'version': '10.5(2)'}, {'status': 'affected', 'version': '10.3(7)'}, {'status': 'affected', 'version': '10.4(5)'}, {'status': 'affected', 'version': '10.5(3)'}, {'status': 'affected', 'version': '10.2(9)'}, {'status': 'affected', 'version': '10.4(4g)'}, {'status': 'affected', 'version': '10.6(1)'}, {'status': 'affected', 'version': '10.5(3t)'}, {'status': 'affected', 'version': '10.3(8)'}, {'status': 'affected', 'version': '10.4(6)'}, {'status': 'affected', 'version': '10.5(3s)'}, {'status': 'affected', 'version': '10.5(3e)'}, {'status': 'affected', 'version': '10.5(3o)'}, {'status': 'affected', 'version': '10.6(1s)'}, {'status': 'affected', 'version': '10.5(3p)'}], 'defaultStatus': 'unknown'}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-20171', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-05-20T18:31:37.215391Z'} -
New CVE Received by [email protected]
May. 20, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H Added CWE CWE-670 Added Reference https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-iefab-3hb2pwtx