CVE-2026-20171: Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
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 Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-20171?
CVE-2026-20171 is classified as a denial of service vulnerability affecting Cisco Nexus 3000 and 9000 Series Switches.
How do I fix CVE-2026-20171?
To fix CVE-2026-20171, apply the recommended software updates from Cisco that address the vulnerability.
What does CVE-2026-20171 affect?
CVE-2026-20171 affects Cisco Nexus 3000 Series and Nexus 9000 Series Switches operating in standalone NX-OS mode.
What can exploit CVE-2026-20171?
CVE-2026-20171 can be exploited by unauthenticated attackers to cause a denial of service condition through the BGP enforce-first-as feature.
Is there a workaround for CVE-2026-20171?
Currently, Cisco has not provided specific workarounds for CVE-2026-20171; the best approach is to update to the patched version.