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

Overview

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.

Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

This advisory is part of the February 2026 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: February 2026 Semiannual Cisco FXOS and NX-OS Software Security Advisory Bundled Publication ["https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75740"].

Vendor advisories

• cisco-sa-nxos-ether-dos-Kv8YNWZ4 · Cisco · affected: Cisco Nexus 3000 Series Switches, Cisco Nexus 9000 Series Switches · updated 2026-02-25 · advisory

Cisco Nexus 3600 and 9500-R Series Switching Platforms Layer 2 Loop Denial of Service Vulnerability. Released 2026-02-25.

Affected:

• Cisco Nexus 3000 Series Switches
• Cisco Nexus 9000 Series Switches

Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com