CVE-2026-20051

Cisco Nexus 3600-R and 9500-R Series Switching Platforms Layer 2 Loop Denial of Service Vulnerability

Published Feb 25, 2026 CVSS 3.1 · 7.4 High EPSS < 1% KEV · Not listed

Description

A vulnerability with the Ethernet VPN (EVPN) Layer 2 ingress packet processing of Cisco Nexus 3600 Platform Switches and Cisco Nexus 9500-R Series Switching Platforms could allow an unauthenticated, adjacent attacker to trigger a Layer 2 traffic loop.

This vulnerability is due to a logic error when processing a crafted Layer 2 ingress frame. An attacker could exploit this vulnerability by sending a stream of crafted Ethernet frames through the targeted device. A successful exploit could allow the attacker to cause a Layer 2 Virtual eXtensible LAN (VxLAN) traffic loop, which, in turn, could result in a denial of service (DoS) condition. This Layer 2 loop could oversubscribe the bandwidth on network interfaces, which would result in all data plane traffic being dropped. To exploit this vulnerability, the attacker must be Layer 2-adjacent to the affected device.
Note: To stop active exploitation of this vulnerability, manual intervention is required to both stop the crafted traffic and flap all involved network interfaces. For additional assistance if a Layer 2 loop that is related to this vulnerability is suspected, contact the Cisco Technical Assistance Center (TAC) or the proper support provider. 

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Cisco

Cisco NX-OS Software

unknown

Version	Status	Constraints
`9.2(3)`	affected	—
`9.2(2v)`	affected	—
`9.2(1)`	affected	—
`9.2(2t)`	affected	—
`9.2(3y)`	affected	—
`9.3(2)`	affected	—
`9.2(4)`	affected	—
`9.3(1)`	affected	—
`9.3(1z)`	affected	—
`9.2(2)`	affected	—
`9.3(3)`	affected	—
`9.3(4)`	affected	—
`9.3(5)`	affected	—
`9.3(6)`	affected	—
`9.3(5w)`	affected	—
`9.3(7)`	affected	—
`9.3(7k)`	affected	—
`10.2(1)`	affected	—
`9.3(7a)`	affected	—
`9.3(8)`	affected	—
`10.2(1q)`	affected	—
`10.2(2)`	affected	—
`9.3(9)`	affected	—
`10.2(3)`	affected	—
`10.2(3t)`	affected	—
`9.3(10)`	affected	—
`10.2(2a)`	affected	—
`10.3(1)`	affected	—
`10.2(4)`	affected	—
`10.3(2)`	affected	—
`9.3(11)`	affected	—
`10.3(3)`	affected	—
`10.2(5)`	affected	—
`9.3(12)`	affected	—
`10.2(3v)`	affected	—
`10.4(1)`	affected	—
`10.2(6)`	affected	—
`10.3(3w)`	affected	—
`10.3(3o)`	affected	—
`10.3(4)`	affected	—
`10.3(3p)`	affected	—
`10.3(4a)`	affected	—
`10.4(2)`	affected	—
`10.3(3q)`	affected	—
`9.3(13)`	affected	—
`10.3(5)`	affected	—
`10.2(7)`	affected	—
`10.4(3)`	affected	—
`10.3(3x)`	affected	—
`10.3(4g)`	affected	—
`10.5(1)`	affected	—
`10.2(8)`	affected	—
`10.3(3r)`	affected	—
`10.3(6)`	affected	—
`9.3(14)`	affected	—
`10.4(4)`	affected	—
`10.3(4h)`	affected	—
`10.5(2)`	affected	—
`10.3(7)`	affected	—
`10.4(5)`	affected	—
`10.5(3)`	affected	—
`10.2(9)`	affected	—
`9.3(15)`	affected	—
`10.4(4g)`	affected	—
`10.5(4)`	affected	—
`10.6(1)`	affected	—
`10.5(3t)`	affected	—
`10.3(8)`	affected	—
`10.4(6)`	affected	—
`10.5(3s)`	affected	—
`10.5(3e)`	affected	—
`10.5(3o)`	affected	—
`9.3(16)`	affected	—
`10.6(1s)`	affected	—
`10.5(3p)`	affected	—

No data.

Vendor Product Versions

Cisco

Nx-os Software

Version	Status	Scheme	Platform
`9.2(3)`	affected	generic	—
`9.2(2v)`	affected	generic	—
`9.2(1)`	affected	generic	—
`9.2(2t)`	affected	generic	—
`9.2(3y)`	affected	generic	—
`9.3(2)`	affected	generic	—
`9.2(4)`	affected	generic	—
`9.3(1)`	affected	generic	—
`9.3(1z)`	affected	generic	—
`9.2(2)`	affected	generic	—
`9.3(3)`	affected	generic	—
`9.3(4)`	affected	generic	—
`9.3(5)`	affected	generic	—
`9.3(6)`	affected	generic	—
`9.3(5w)`	affected	generic	—
`9.3(7)`	affected	generic	—
`9.3(7k)`	affected	generic	—
`10.2(1)`	affected	generic	—
`9.3(7a)`	affected	generic	—
`9.3(8)`	affected	generic	—
`10.2(1q)`	affected	generic	—
`10.2(2)`	affected	generic	—
`9.3(9)`	affected	generic	—
`10.2(3)`	affected	generic	—
`10.2(3t)`	affected	generic	—
`9.3(10)`	affected	generic	—
`10.2(2a)`	affected	generic	—
`10.3(1)`	affected	generic	—
`10.2(4)`	affected	generic	—
`10.3(2)`	affected	generic	—
`9.3(11)`	affected	generic	—
`10.3(3)`	affected	generic	—
`10.2(5)`	affected	generic	—
`9.3(12)`	affected	generic	—
`10.2(3v)`	affected	generic	—
`10.4(1)`	affected	generic	—
`10.2(6)`	affected	generic	—
`10.3(3w)`	affected	generic	—
`10.3(3o)`	affected	generic	—
`10.3(4)`	affected	generic	—
`10.3(3p)`	affected	generic	—
`10.3(4a)`	affected	generic	—
`10.4(2)`	affected	generic	—
`10.3(3q)`	affected	generic	—
`9.3(13)`	affected	generic	—
`10.3(5)`	affected	generic	—
`10.2(7)`	affected	generic	—
`10.4(3)`	affected	generic	—
`10.3(3x)`	affected	generic	—
`10.3(4g)`	affected	generic	—
`10.5(1)`	affected	generic	—
`10.2(8)`	affected	generic	—
`10.3(3r)`	affected	generic	—
`10.3(6)`	affected	generic	—
`9.3(14)`	affected	generic	—
`10.4(4)`	affected	generic	—
`10.3(4h)`	affected	generic	—
`10.5(2)`	affected	generic	—
`10.3(7)`	affected	generic	—
`10.4(5)`	affected	generic	—
`10.5(3)`	affected	generic	—
`10.2(9)`	affected	generic	—
`9.3(15)`	affected	generic	—
`10.4(4g)`	affected	generic	—
`10.5(4)`	affected	generic	—
`10.6(1)`	affected	generic	—
`10.5(3t)`	affected	generic	—
`10.3(8)`	affected	generic	—
`10.4(6)`	affected	generic	—
`10.5(3s)`	affected	generic	—
`10.5(3e)`	affected	generic	—
`10.5(3o)`	affected	generic	—
`9.3(16)`	affected	generic	—
`10.6(1s)`	affected	generic	—
`10.5(3p)`	affected	generic	—
`10.5(3t)`	affected	generic	—
`10.5(3t)`	affected	generic	—

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

No advisories available

Metrics

No CVSS v4.0

Attack Vector Adjacent Network

Attack Complexity Low

Privileges Required None

Scope Changed

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.173% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

Link	Providers
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ether-dos-Kv8YNWZ4

History

Nov 10, 2026 9:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Feb 26, 2026 1:30 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Cisco Cisco nx-os Software
Vendors & Products		Cisco Cisco nx-os Software

Feb 25, 2026 4:45 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		A vulnerability with the Ethernet VPN (EVPN) Layer 2 ingress packet processing of Cisco Nexus 3600 Platform Switches and Cisco Nexus 9500-R Series Switching Platforms could allow an unauthenticated, adjacent attacker to trigger a Layer 2 traffic loop. This vulnerability is due to a logic error when processing a crafted Layer 2 ingress frame. An attacker could exploit this vulnerability by sending a stream of crafted Ethernet frames through the targeted device. A successful exploit could allow the attacker to cause a Layer 2 Virtual eXtensible LAN (VxLAN) traffic loop, which, in turn, could result in a denial of service (DoS) condition. This Layer 2 loop could oversubscribe the bandwidth on network interfaces, which would result in all data plane traffic being dropped. To exploit this vulnerability, the attacker must be Layer 2-adjacent to the affected device. Note: To stop active exploitation of this vulnerability, manual intervention is required to both stop the crafted traffic and flap all involved network interfaces. For additional assistance if a Layer 2 loop that is related to this vulnerability is suspected, contact the Cisco Technical Assistance Center (TAC) or the proper support provider.
Title		Cisco Nexus 3600-R and 9500-R Series Switching Platforms Layer 2 Loop Denial of Service Vulnerability
Weaknesses		CWE-457
References		https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ether-dos-Kv8YNWZ4
Metrics		cvssV3_1 `{'score': 7.4, 'vector': 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H'}`