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.

No CVSS v4.0

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Changed

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00035.

Exploitation none

Automatable no

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
Cisco Cisco NX-OS Software unknown
Version Status Constraints
10.2(1) affected —
10.2(1q) affected —
10.2(2) affected —
10.2(3) affected —
10.2(3t) affected —
10.2(2a) affected —
10.3(1) affected —
10.2(4) affected —
10.3(2) affected —
10.3(3) affected —
10.2(5) affected —
10.2(3v) affected —
10.4(1) affected —
10.3(99w) affected —
10.2(6) affected —
10.3(3w) affected —
10.3(99x) affected —
10.3(3o) affected —
10.3(4) affected —
10.3(3p) affected —
10.3(4a) affected —
10.4(2) affected —
10.3(3q) affected —
10.3(5) affected —
10.2(7) affected —
10.4(3) affected —
10.3(3x) affected —
10.3(4g) affected —
10.5(1) affected —
10.2(8) affected —
10.3(3r) affected —
10.3(6) affected —
10.4(4) affected —
10.3(4h) affected —
10.5(2) affected —
10.3(7) affected —
10.4(5) affected —
10.5(3) affected —
10.2(9) affected —
10.4(4g) affected —
10.6(1) affected —
10.5(3t) affected —
10.3(8) affected —
10.4(6) affected —
10.5(3s) affected —
10.5(3e) affected —
10.5(3o) affected —
10.6(1s) affected —
10.5(3p) affected —

No data.

No data.

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Advisories

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Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-iefab-3hb2pwtx cve-icon cve-icon
History

Thu, 21 May 2026 08:30:00 +0000

Type Values Removed Values Added
First Time appeared Cisco
Cisco nx-os Software
Vendors & Products Cisco
Cisco nx-os Software

Wed, 20 May 2026 20:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 20 May 2026 16:45:00 +0000

Type Values Removed Values 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.
Title Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
Weaknesses CWE-670
References
Metrics cvssV3_1

{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: cisco

Published:

Updated: 2026-05-20T18:31:44.204Z

Reserved: 2025-10-08T11:59:15.391Z

Link: CVE-2026-20171

cve-icon Vulnrichment

Updated: 2026-05-20T18:31:40.918Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-05-20T17:16:19.813

Modified: 2026-05-20T17:30:40.450

Link: CVE-2026-20171

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-21T08:15:06Z

Weaknesses