CVE-2026-20171
Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
- 6.8MediumCVSS base score
- 0.47%Exploitation in 30 daysEPSS · top 59% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By cisco
- 7 months later
· 7 months later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| ciscoCNA (assigner) | 3.1 | Medium6.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
| NVDNVD · Awaiting Analysis | 3.1 | Medium6.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.47% · top 59% of all CVEs (11 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.8.
Affected products
- affected 10.2(1)
- affected 10.2(1q)
- affected 10.2(2)
- affected 10.2(3)
- affected 10.2(3t)
- affected 10.2(2a)
- affected 10.3(1)
- affected 10.2(4)
- affected 10.3(2)
- affected 10.3(3)
- affected 10.2(5)
- affected 10.2(3v)
- affected 10.4(1)
- affected 10.3(99w)
- affected 10.2(6)
- affected 10.3(3w)
- affected 10.3(99x)
- affected 10.3(3o)
- affected 10.3(4)
- affected 10.3(3p)
- affected 10.3(4a)
- affected 10.4(2)
- affected 10.3(3q)
- affected 10.3(5)
- affected 10.2(7)
- affected 10.4(3)
- affected 10.3(3x)
- affected 10.3(4g)
- affected 10.5(1)
- affected 10.2(8)
- affected 10.3(3r)
- affected 10.3(6)
- affected 10.4(4)
- affected 10.3(4h)
- affected 10.5(2)
- affected 10.3(7)
- affected 10.4(5)
- affected 10.5(3)
- affected 10.2(9)
- affected 10.4(4g)
- and 9 more
What to do
Exploitation: The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
References
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-31135 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-20171)Record last updated .