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Nx OsOperating system · Cisco

CVE-2021-1228

MEDIUM · 6.5 CVSS v3.1 Published 2021-02-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This vulnerability in Cisco Nexus 9000 Series Fabric Switches in ACI Mode allows an adjacent unauthenticated attacker to bypass security checks during the LLDP (Link Layer Discovery Protocol) setup phase for infrastructure VLAN connections. By sending crafted LLDP packets on the adjacent subnet, an attacker can connect an unauthorized server to the privileged infrastructure VLAN, enabling unauthorized access to APIC services and other host endpoints.

MitigationApply Cisco's firmware update for this vulnerability; as an interim measure, consider disabling LLDP on ports facing untrusted segments or implementing port-based access controls to limit which devices can participate in LLDP discovery.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nx OsOperating system
Affected:= 11.0\(1b\)= 11.0\(1c\)= 11.0\(1d\)= 11.0\(1e\)= 11.0\(2j\)= 11.0\(2m\)= 11.0\(3f\)= 11.0\(3i\)= 11.0\(3k\)= 11.0\(3n\)= 11.0\(3o\)= 11.0\(4g\)

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the device model and mode
    Run 'show version' or 'show inventory' to confirm the device is a Cisco Nexus 9000 Series Fabric Switch running in ACI Mode
    Affected if Device is a Nexus 9000 Series in ACI Mode
  2. Check the NX-OS version
    Run 'show version' and locate the NX-OS release string (e.g., 11.0(1b), 11.0(2j), etc.)
    Affected if Installed version matches exactly one of these: 11.0(1b), 11.0(1c), 11.0(1d), 11.0(1e), 11.0(2j), 11.0(2m), 11.0(3f), 11.0(3i), 11.0(3k), 11.0(3n), 11.0(3o), 11.0(4g)
  3. Verify LLDP is enabled
    Run 'show lldp status' or 'show running-config | include lldp' to determine if LLDP is globally enabled or enabled on specific interfaces
    Affected if LLDP is enabled on any interface facing untrusted segments or the infrastructure VLAN
  4. Check infrastructure VLAN configuration
    Run 'show vlan' and 'show running-config | section vlan' to identify infrastructure VLANs used for APIC connectivity
    Affected if Infrastructure VLANs (typically VLAN 1 or dedicated management VLANs in ACI) are present and accessible via LLDP-enabled ports

You are affected if you are running a Nexus 9000 Series switch in ACI Mode with any of the listed NX-OS versions AND LLDP is enabled on ports that connect to untrusted network segments.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco's firmware update for this vulnerability; as an interim measure, consider disabling LLDP on ports facing untrusted segments or implementing port-based access controls to limit which devices can participate in LLDP discovery.

Fix this in Nx Os Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing10.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,580
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-1228 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data