What is CVE-2021-1231?

CVE-2021-1231 is a medium-severity vulnerability in Cisco Nx-Os System Software In Aci Mode, classified under Improper Access Control. CVSS score: 4.7/10. Published 2021-02-24.

How severe is CVE-2021-1231?

Medium severity. CVSS v3 base score is 4.7 out of 10.

Vulnerability in Cisco Nx-Os System Software In Aci Mode

CVE-2021-1231

A vulnerability in the Link Layer Discovery Protocol (LLDP) for Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode could allow an unauthenticated, adjacent attacker to disable switching on a small form-factor pluggable (SFP) interface. This vulnerability is due to incomplete validation of the source of a received LLDP packet. An attacker could exploit this vulnerability by sending a crafted LLDP packet on an SFP interface to an affected device. A successful exploit could allow the attacker to disable switching on the SFP interface, which could disrupt network traffic.

Published 2021-02-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.7 (Medium). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.003 (15.7th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 15.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Weakness classification (CWE)

References

tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apic-lld… (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2021-1231?: CVE-2021-1231 is a medium-severity vulnerability in Cisco Nx-Os System Software In Aci Mode, classified under Improper Access Control. CVSS score: 4.7/10. Published 2021-02-24.
How severe is CVE-2021-1231?: Medium severity. CVSS v3 base score is 4.7 out of 10.