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.
Weakness: CWE-670
Affected products
| Vendor | Product | Category | Matched by |
|---|---|---|---|
| Cisco | Cisco NX-OS Software | Routing & Switching | cna-assigner |
Vendor-reported products (1)
- Cisco · Cisco NX-OS Software
Vendor advisory
Cisco Nexus 3000 and 9000 Series Switches Border Gateway Protocol Denial of Service Vulnerability
Cisco’s rating: Medium (advisory CVSS 6.8) · Published May 20, 2026
Bug ID: CSCwr23951
The vendor’s rating applies to the whole advisory and can differ from this CVE’s own CVSS severity. Where this comes from