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Nx OsOperating system · Cisco

CVE-2019-1977

HIGH · 7.5 CVSS v3.0 Published 2019-08-30
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable 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 within the Endpoint Learning feature of Cisco Nexus 9000 Series Switches running in Application Centric Infrastructure (ACI) mode could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an endpoint device in certain circumstances. The vulnerability is due to improper endpoint learning when packets are received on a specific port from outside the ACI fabric and destined to an endpoint located on a border leaf when Disable Remote Endpoint Learning has been enabled. This can result in a Remote (XR) entry being created for the impacted endpoint that will become stale if the endpoint migrates to a different port or leaf switch. This results in traffic not reaching the impacted endpoint until the Remote entry can be relearned by another mechanism.

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

A vulnerability in Cisco Nexus 9000 Series Switches running in ACI mode allows unauthenticated remote attackers to cause DoS via the Endpoint Learning feature. When Disable Remote Endpoint Learning is enabled, packets from outside the ACI fabric destined to an endpoint on a border leaf create a stale Remote (XR) entry that prevents traffic from reaching the endpoint if the endpoint migrates to a different port or leaf switch.

MitigationReview the Disable Remote Endpoint Learning configuration on affected border leaf switches and consider disabling this feature if appropriate, or apply Cisco's recommended updates if available.

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:= 12.3\(1h\)= 13.1\(2m\)= 13.1\(2o\)= 13.1\(2p\)

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 Switch. Run 'show fabric mode' or 'show acitopology' to confirm it is running in ACI mode.
    Affected if Device is a Nexus 9000 Series Switch NOT running in ACI mode, then this CVE does not apply.
  2. Check the NX-OS version
    Run 'show version' and locate the installed NX-OS version. Compare it against the affected versions: 12.3(1h), 13.1(2m), 13.1(2o), 13.1(2p).
    Affected if Installed version matches exactly one of the affected versions listed.
  3. Verify if Disable Remote Endpoint Learning is configured
    Run 'show running-config | include endpoint learning' or 'show endpoint interface' to check the Endpoint Learning configuration. Look for the 'Disable Remote Endpoint Learning' setting on border leaf switches.
    Affected if Disable Remote Endpoint Learning is enabled on the border leaf switch.
  4. Inspect for stale Remote (XR) entries
    Run 'show endpoint' or 'show endpoint remote' to view Remote (XR) entries. Look for entries associated with external interfaces that may be stale after endpoint migration.
    Affected if Stale Remote (XR) entries exist showing endpoints that have migrated to different ports or leaf switches.

You are affected if you have a Nexus 9000 switch in ACI mode running one of the exact affected versions (12.3(1h), 13.1(2m), 13.1(2o), or 13.1(2p) with Disable Remote Endpoint Learning enabled on a border leaf.

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

Review the Disable Remote Endpoint Learning configuration on affected border leaf switches and consider disabling this feature if appropriate, or apply Cisco's recommended updates if available.

Fix this in Nx Os Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
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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-2019-1977 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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