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Nx OsOperating system · Cisco

CVE-2020-3338

HIGH · 7.5 CVSS v3.1 Published 2020-08-27
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 in the Protocol Independent Multicast (PIM) feature for IPv6 networks (PIM6) of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper error handling when processing inbound PIM6 packets. An attacker could exploit this vulnerability by sending multiple crafted PIM6 packets to an affected device. A successful exploit could allow the attacker to cause the PIM6 application to leak system memory. Over time, this memory leak could cause the PIM6 application to stop processing legitimate PIM6 traffic, leading to a DoS condition on the affected device.

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 is a memory leak vulnerability in Cisco NX-OS Software's Protocol Independent Multicast for IPv6 (PIM6) feature. The vulnerability stems from improper error handling when processing inbound PIM6 packets, allowing an unauthenticated remote attacker to send crafted PIM6 packets that cause the PIM6 application to leak system memory. Over time, this exhausts resources and prevents the PIM6 application from processing legitimate traffic, resulting in a denial of service.

MitigationApply the Cisco-provided patch for NX-OS when available. If no patch exists, consider disabling PIM6 if not required, or implement network segmentation to limit exposure to unauthenticated PIM6 packet sources.

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:all versions

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:3.1/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. Confirm Cisco NX-OS platform
    Run 'show version' or 'show inventory' to verify the device runs Cisco NX-OS software
    Affected if Device is running any version of Cisco NX-OS software
  2. Check if PIM6 is enabled
    Run 'show ip pim vrf all ipv6' or 'show ipv6 pim interface' to list active PIM6 interfaces
    Affected if PIM6 is enabled on any interface (the vulnerability only triggers when PIM6 processes inbound packets)
  3. Verify PIM6 process is running
    Run 'show process cpu | include pim6' or 'show system internal processes memory | grep pim6' to confirm the PIM6 daemon is active
    Affected if PIM6 process is actively running on the system
  4. Check for PIM6-related error logs
    Run 'show logging | include PIM6|pim6' or check the system log buffer for PIM6 packet processing errors
    Affected if Logs show repeated PIM6 packet errors or warnings about malformed packets
  5. Monitor memory usage of PIM6 process
    Run 'show system internal processes memory detail | grep pim6' over time to observe if memory usage is steadily increasing
    Affected if PIM6 process shows abnormally high or continuously growing memory consumption

Any Cisco NX-OS device with PIM6 enabled is affected by this vulnerability, since all versions of NX-OS are impacted and the flaw only manifests when the PIM6 feature processes inbound packets.

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 the Cisco-provided patch for NX-OS when available. If no patch exists, consider disabling PIM6 if not required, or implement network segmentation to limit exposure to unauthenticated PIM6 packet sources.

Fix this in Nx Os Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
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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-2020-3338 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
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  • No spam, self-promotion, credentials, or personal data