CVE-2026-20171 Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
Remote attackers can cause denial of service on Cisco Nexus switches by sending crafted BGP updates when enforce-first-as is enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20171?
CVE-2026-20171 is a medium-severity denial of service vulnerability in Cisco NX-OS Software, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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
Which versions are affected by CVE-2026-20171?
How do I fix CVE-2026-20171?
No fix has been published for CVE-2026-20171 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-20171 being exploited?
There is no known exploitation of CVE-2026-20171 in the wild and no public exploit code.
Sources
Also known as GHSA-h75f-8f3x-9m8c.