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CVE Record

CVE-2021-1228: Cisco Nexus 9000 Series Fabric Switches ACI Mode Fabric Infrastructure VLAN Unauthorized Access Vulnerability

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.

HighCVSS 7.4Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw affects Cisco Nexus 9000 switches running ACI mode. A nearby unauthenticated attacker could abuse LLDP setup behavior to attach an unauthorized server to the highly privileged fabric infrastructure VLAN, creating a path toward APIC services or other endpoints.

Executive priority

Treat as high priority where ACI fabric ports or adjacent Layer 2 networks are not tightly controlled. The main business risk is unauthorized access into privileged fabric infrastructure, not broad internet exposure.

Technical view

The issue is insufficient security validation during infrastructure VLAN establishment in the LLDP setup phase. CVSS 3.1 is 7.4, adjacent network attack vector, low complexity, no privileges or user interaction, changed scope, and high integrity impact.

Likely exposure

Exposure is limited to Cisco Nexus 9000 Series Fabric Switches in ACI Mode matching affected Cisco NX-OS ACI software. Organizations without ACI-mode Nexus 9000 fabrics are unlikely to be affected based on the supplied sources.

Exploitation context

The supplied sources describe a crafted LLDP packet from an adjacent subnet. They do not show active exploitation, and the CVE is not marked as CISA KEV in the bundle.

Researcher notes

This is a CWE-284 authorization/control weakness in infrastructure VLAN onboarding logic. Validation should focus on affected ACI-mode software, LLDP adjacency trust boundaries, and evidence of unauthorized infrastructure VLAN membership without performing exploit reproduction.

Mitigation direction

  • Identify Nexus 9000 switches running ACI mode.
  • Review Cisco advisory guidance for fixed software or mitigations.
  • Prioritize remediation on fabrics with untrusted adjacent access.
  • Restrict physical and Layer 2 adjacency to trusted infrastructure.
  • Monitor for unauthorized infrastructure VLAN associations.

Validation and detection

  • Inventory ACI-mode Nexus 9000 devices and software versions.
  • Compare versions against Cisco advisory affected and fixed release guidance.
  • Review infrastructure VLAN access for unexpected attached hosts.
  • Check APIC service reachability from unauthorized adjacent segments.
  • Confirm LLDP exposure is limited to trusted links.
Prepared
Confidence
medium
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · medium confidence lookup

CWE-284: Authorization and privilege behavior lookup

Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2021-1228 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.4 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.4CVSS 3.1HighCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N2.84Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.4High
CVSS 3.1 vector shape for CVE-2021-1228Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
CiscoCisco NX-OS System Software in ACI Mode 11.0(1b)n/aListed
Weakness

CWE details

CWE-284

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-284 · source CWE mapping

Improper Access Control

Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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