Cisco Nexus 9000 Series Fabric Switches ACI Mode Fabric Infrastructure VLAN Unauthorized Access Vulnerability

published 2021-02-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-6695

cvss: 7.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 32%
public exploits: 0; none known

A vulnerability in the fabric infrastructure VLAN connection establishment of Cisco Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) Mode could allow an unauthenticated, adjacent attacker to bypass security validations and connect an unauthorized server to the infrastructure VLAN. This vulnerability is due to insufficient security requirements during the Link Layer Discovery Protocol (LLDP) setup phase of the infrastructure VLAN. An attacker could exploit this vulnerability by sending a crafted LLDP packet on the adjacent subnet to an affected device. A successful exploit could allow the attacker to connect an unauthorized server to the infrastructure VLAN, which is highly privileged. With a connection to the infrastructure VLAN, the attacker can make unauthorized connections to Cisco Application Policy Infrastructure Controller (APIC) services or join other host endpoints.

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 y ago (2024-11-08)

Exploit prediction

0.39% chance of exploitation in the next 30 days, higher than 32% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.4	CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
NVD	3.1	6.5	CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD	2.0	3.3	AV:A/AC:L/Au:N/C:N/I:P/A:N

Affected products

Cisco Cisco NX-OS System Software in ACI Mode 11.0(1b)

Classification

Weakness

CWE-284 Improper Access Control

References

tools.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-n9kaci-unauth-access-5PWzDx2w
vendor-advisory

Sources

CVE List CVE-2021-1228
NVD CVE-2021-1228

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Summary