dbcve.org
Nx OsOperating system · Cisco

CVE-2020-3398

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 a BGP session to repeatedly reset, causing a partial denial of service (DoS) condition due to the BGP session being down. The vulnerability is due to incorrect parsing of a specific type of BGP MVPN update message. An attacker could exploit this vulnerability by sending this BGP MVPN update message to a targeted device. A successful exploit could allow the attacker to cause the BGP peer connections to reset, which could lead to BGP route instability and impact traffic. The incoming BGP MVPN update message is valid but is parsed incorrectly by the NX-OS device, which could send a corrupted BGP update to the configured BGP peer. 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 BGP sessions to repeatedly reset by sending a specifically crafted BGP MVPN update message. The device incorrectly parses this valid message, sending corrupted BGP updates to peers and causing BGP route instability and partial DoS.

MitigationApply Cisco-provided NX-OS patches addressing this vulnerability; implement BGP MD5 authentication and control-plane filtering to prevent malicious MVPN updates from untrusted 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
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. Check NX-OS version
    Run 'show version' command on the Cisco NX-OS device to identify the installed version
    Affected if Any version of Cisco NX-OS is running (all versions are affected)
  2. Verify BGP is enabled
    Run 'show bgp summary' or 'show ip bgp summary' to confirm BGP is configured and active
    Affected if BGP is running and peers exist on the device
  3. Check for BGP MVPN address family configuration
    Run 'show bgp vpnv4 unicast all' or 'show bgp vrf all' to see if BGP VPN address families are configured; then check for MVPN-specific configuration with 'show running-config | include mvpn' or 'show bgp vpnv4 unicast all update-group' to see MVPN updates
    Affected if BGP MVPN (Multicast VPN) address family is enabled on any BGP neighbor or VRF
  4. Inspect BGP MVPN peers and updates
    Run 'show bgp vpnv4 unicast all neighbors' and look for 'mvpn' in the output, or check 'show bgp peer-session' and 'show bgp peer-template' for MVPN configuration
    Affected if Any BGP peer is configured to exchange MVPN routes or updates

The device is affected if it runs any version of Cisco NX-OS with BGP MVPN feature enabled, as the vulnerability is triggered by processing crafted MVPN update messages on such configurations.

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-provided NX-OS patches addressing this vulnerability; implement BGP MD5 authentication and control-plane filtering to prevent malicious MVPN updates from untrusted sources.

Fix this in Nx Os Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2020-3398 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
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  • Version or environment caveats, and links to real fixes
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