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Nx OsOperating system · Cisco

CVE-2020-3397

HIGH · 8.6 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 →
95/100
Remediation priority · Urgent
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 Border Gateway Protocol (BGP) Multicast VPN (MVPN) implementation of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause an affected device to unexpectedly reload, resulting in a denial of service (DoS) condition. The vulnerability is due to incomplete input validation of a specific type of BGP MVPN update message. An attacker could exploit this vulnerability by sending this specific, valid BGP MVPN update message to a targeted device. A successful exploit could allow the attacker to cause one of the BGP-related routing applications to restart multiple times, leading to a system-level restart. Note: The Cisco implementation of BGP accepts incoming BGP traffic from only explicitly configured peers. To exploit this vulnerability, an attacker must send a specific BGP MVPN update message over an established TCP connection that appears to come from a trusted BGP peer. To do so, the attacker must obtain information about the BGP peers in the trusted network of the affected system.

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 NX-OS BGP Multicast VPN (MVPN) implementation allows an unauthenticated remote attacker to cause device reload and DoS by sending a specific valid BGP MVPN update message over a TCP connection appearing to originate from a trusted BGP peer. The attacker requires prior knowledge of BGP peer information in the trusted network.

MitigationApply Cisco's NX-OS software update when available. In the interim, implement BGP MD5 authentication between peers and use ACLs to restrict BGP traffic to known, trusted peers to prevent spoofed connection attacks.

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
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 is running
    Run 'show version' or check the device model/type to verify it is a Cisco NX-OS system
    Affected if The device runs any version of Cisco NX-OS software
  2. Verify BGP is enabled
    Run 'show bgp summary' or 'show ip bgp summary' to check if BGP is configured and active
    Affected if BGP is configured and running on the NX-OS device
  3. Check if BGP MVPN feature is enabled
    Run 'show vrf' or 'show bgp mvpn' to determine if any MVPN VRFs are configured
    Affected if BGP MVPN is configured and actively running on the device
  4. Confirm BGP MD5 authentication is absent
    Run 'show bgp neighbor' and inspect the BGP neighbor configuration for authentication settings; check configuration with 'show run bgp' to see if 'neighbor X.X.X.X password' or 'md5' is configured
    Affected if BGP peers do NOT have MD5 authentication configured and are reachable over TCP from untrusted networks

The device is affected if it runs Cisco NX-OS with BGP enabled and MVPN configured while lacking BGP MD5 authentication between peers, allowing potential spoofed BGP MVPN messages from attackers with knowledge of the trusted peer configuration.

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 NX-OS software update when available. In the interim, implement BGP MD5 authentication between peers and use ACLs to restrict BGP traffic to known, trusted peers to prevent spoofed connection attacks.

Fix this in Nx Os Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,780
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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-2020-3397 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