Security readout for executives and security teams
Plain-English summary
This Cisco NX-OS flaw can let a remote unauthenticated attacker disrupt affected network switches in a VXLAN EVPN fabric. Successful abuse can drive high CPU use, destabilize the control plane, and trigger device reloads. Business impact is availability: traffic disruption and operational instability. The NGOAM feature is disabled by default, which reduces likely exposure.
Executive priority
Treat this as a high-priority availability risk for Cisco VXLAN EVPN environments. It is most urgent where affected switches support critical production networks and NGOAM is enabled. Exposure may be materially lower if NGOAM remains disabled, but owners should verify rather than assume.
Technical view
CVE-2021-1587 affects Cisco NX-OS Software VXLAN OAM, known as NGOAM. Improper handling of packets using the TRILL OAM EtherType 0x8902 can cause excessive resource consumption on devices in a VXLAN EVPN fabric. CVSS 3.1 is 8.6, network exploitable, low complexity, unauthenticated, no user interaction, availability impact high.
Likely exposure
Likely exposure is limited to Cisco NX-OS deployments that are part of a VXLAN EVPN fabric and have NGOAM enabled. The provided source states NGOAM is disabled by default. Organizations without VXLAN EVPN fabric use, or with NGOAM disabled, are less likely to be exposed based on the available evidence.
Exploitation context
The source bundle describes unauthenticated remote denial of service using crafted packets sent to an affected VXLAN EVPN fabric device. It does not provide evidence of active exploitation, and the CVE is not listed as KEV in the provided data.
Researcher notes
The evidence supports a denial-of-service issue in NGOAM packet handling, not data theft or code execution. The bundle does not name fixed versions or non-default mitigations beyond NGOAM being disabled by default. Avoid claims of exploitation unless new KEV or vendor intelligence confirms them.
Mitigation direction
- Confirm whether NGOAM is enabled on Cisco NX-OS VXLAN EVPN fabric devices.
- Keep NGOAM disabled unless it is operationally required.
- Review Cisco’s advisory for affected releases and vendor-supported fixed software.
- Prioritize remediation for fabric devices that protect critical production traffic.
- Monitor affected devices for high CPU, control plane instability, or unexpected reloads.
Validation and detection
- Inventory Cisco NX-OS devices participating in VXLAN EVPN fabrics.
- Check each device configuration for NGOAM feature use.
- Map NX-OS versions against Cisco’s advisory guidance.
- Review device logs for reloads, high CPU, or control plane instability.
- Confirm monitoring covers availability and CPU symptoms on fabric switches.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2021-1587 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210825 Cisco NX-OS Software VXLAN OAM (NGOAM) Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Misinterpretation of Input
Misinterpretation of Input represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.