Vulnerability in Cisco Nx-Os Software
CVE-2026-20171
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 · last modified .
CVSS v3 metric
CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.005 (37.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 38th percentile — 37.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Cisco Nx-Os Software — versions 10.2(1), 10.2(1q), 10.2(2)
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-20171?
- CVE-2026-20171 is a medium-severity vulnerability in Cisco Nx-Os Software, classified under Always-Incorrect Control Flow Implementation. CVSS score: 6.8/10. Published 2026-05-20.
- How severe is CVE-2026-20171?
- Medium severity. CVSS v3 base score is 6.8 out of 10.