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.
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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
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| Cisco | Cisco NX-OS Software | unknown |
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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 | |
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| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: cisco
Published:
Updated: 2026-05-20T16:06:38.711Z
Reserved: 2025-10-08T11:59:15.391Z
Link: CVE-2026-20171
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