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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.

PUBLISHED Reserved 2025-10-08 | Published 2026-05-20 | Updated 2026-05-20 | Assigner cisco




MEDIUM: 6.8CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H

Problem types

Always-Incorrect Control Flow Implementation

Product status

Default status
unknown

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

References

sec.cloudapps.cisco.com/...isory/cisco-sa-bgp-iefab-3hb2pwtx (cisco-sa-bgp-iefab-3hb2pwtx)

cve.org (CVE-2026-20171)

nvd.nist.gov (CVE-2026-20171)

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