# CVE-2026-20171

## Summary

- **CVE ID:** CVE-2026-20171
- **Severity:** MEDIUM
- **CVSS Score:** 6.8 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H)
- **CWE:** CWE-670
- **Published:** May 20, 2026
- **Last Modified:** May 20, 2026

## 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.

## Affected Products

- Cisco — Cisco NX-OS Software (10.2(1))
- Cisco — Cisco NX-OS Software (10.2(1q))
- Cisco — Cisco NX-OS Software (10.2(2))
- Cisco — Cisco NX-OS Software (10.2(3))
- Cisco — Cisco NX-OS Software (10.2(3t))
- Cisco — Cisco NX-OS Software (10.2(2a))
- Cisco — Cisco NX-OS Software (10.3(1))
- Cisco — Cisco NX-OS Software (10.2(4))
- Cisco — Cisco NX-OS Software (10.3(2))
- Cisco — Cisco NX-OS Software (10.3(3))
- Cisco — Cisco NX-OS Software (10.2(5))
- Cisco — Cisco NX-OS Software (10.2(3v))
- Cisco — Cisco NX-OS Software (10.4(1))
- Cisco — Cisco NX-OS Software (10.3(99w))
- Cisco — Cisco NX-OS Software (10.2(6))
- Cisco — Cisco NX-OS Software (10.3(3w))
- Cisco — Cisco NX-OS Software (10.3(99x))
- Cisco — Cisco NX-OS Software (10.3(3o))
- Cisco — Cisco NX-OS Software (10.3(4))
- Cisco — Cisco NX-OS Software (10.3(3p))
- Cisco — Cisco NX-OS Software (10.3(4a))
- Cisco — Cisco NX-OS Software (10.4(2))
- Cisco — Cisco NX-OS Software (10.3(3q))
- Cisco — Cisco NX-OS Software (10.3(5))
- Cisco — Cisco NX-OS Software (10.2(7))
- Cisco — Cisco NX-OS Software (10.4(3))
- Cisco — Cisco NX-OS Software (10.3(3x))
- Cisco — Cisco NX-OS Software (10.3(4g))
- Cisco — Cisco NX-OS Software (10.5(1))
- Cisco — Cisco NX-OS Software (10.2(8))
- Cisco — Cisco NX-OS Software (10.3(3r))
- Cisco — Cisco NX-OS Software (10.3(6))
- Cisco — Cisco NX-OS Software (10.4(4))
- Cisco — Cisco NX-OS Software (10.3(4h))
- Cisco — Cisco NX-OS Software (10.5(2))
- Cisco — Cisco NX-OS Software (10.3(7))
- Cisco — Cisco NX-OS Software (10.4(5))
- Cisco — Cisco NX-OS Software (10.5(3))
- Cisco — Cisco NX-OS Software (10.2(9))
- Cisco — Cisco NX-OS Software (10.4(4g))
- Cisco — Cisco NX-OS Software (10.6(1))
- Cisco — Cisco NX-OS Software (10.5(3t))
- Cisco — Cisco NX-OS Software (10.3(8))
- Cisco — Cisco NX-OS Software (10.4(6))
- Cisco — Cisco NX-OS Software (10.5(3s))
- Cisco — Cisco NX-OS Software (10.5(3e))
- Cisco — Cisco NX-OS Software (10.5(3o))
- Cisco — Cisco NX-OS Software (10.6(1s))
- Cisco — Cisco NX-OS Software (10.5(3p))

## References

- [CNA](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-iefab-3hb2pwtx)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.47%
- **EPSS Percentile:** 39.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._