External risk intelligence

Cisco Nexus 9000 Silicon One RCE via Exposed TCP Ports

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-20212

The vulnerability affects Cisco Nexus 9000 Series Switches and involves TCP ports 43210 and 43211 being exposed in the default Layer 3 virtual routing and forwarding. These switches are commonly deployed as network infrastructure and edge devices, making them reachable if these ports are not explicitly blocked or firewalled from the public internet.

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in Cisco Nexus 9000 Series Switches, specifically within the Silicon One integration. This issue could permit an unauthenticated attacker to remotely execute code with the highest level of system privileges, potentially leading to device reloads and disruption of network services. The primary concern is to confirm if our specific network infrastructure is exposed and affected by this vulnerability.

Unauthenticated code execution on network devices.
Critical network infrastructure could be compromised remotely.
Confirm relevance and exposure to affected systems.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker could exploit this vulnerability by connecting to exposed TCP ports on Cisco Nexus 9000 Series Switches. By sending specially crafted input to these ports, an attacker could execute arbitrary code with root privileges, potentially leading to a device reload.

Network access to specific TCP ports is required.
Sending crafted input to TCP ports 43210 or 43211 triggers the vulnerability.
Risk of remote code execution with root privileges.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated, remote attacker to execute arbitrary code with root privileges on Cisco Nexus 9000 Series Switches when TCP ports 43210 and 43211 are accessible in the default Layer 3 VRF. Successful exploitation may lead to the S1HAL process crashing, potentially causing the device to reload.

Root access to network infrastructure.
Crafted input sent over exposed TCP ports.
Device reload, impacting network services.

Operational Fix

Recommended remediation, mitigation, and detection steps

Real-world responsibility for this critical vulnerability likely falls to network and infrastructure teams, who manage Cisco Nexus 9000 Series Switches. The first step is to identify all instances of the affected technology, determine their exposure and business criticality, and then coordinate remediation with the accountable owners.

Network and infrastructure teams own resolution.
Verify external reachability of TCP ports 43210/43211.
Plan remediation based on exposure and criticality.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the Cisco Nexus 9000 Series and how is it used?

These are high-performance switches designed for data centers and large-scale enterprise networks. They move traffic between servers and network segments. This specific vulnerability involves the Silicon One component, a specialized processor architecture integrated into the hardware to handle high-speed data switching and routing tasks.

What does CVE-2026-20212 mean in plain English?

This is a critical security weakness categorized as CWE-1327, which relates to improper restriction of communication channels. In this case, specific network ports meant for internal management are left accessible in a way that allows anyone on the network to talk to them without proving who they are. Because these ports have high-level system access, an attacker can send malicious commands to take full control of the device.

How does an attacker trigger this vulnerability?

An attacker triggers the bug by sending specially crafted data packets to TCP ports 43210 or 43211 on an affected switch. The vulnerability specifically requires access to these ports within the default Layer 3 virtual routing and forwarding (VRF) instance. It is not triggered by standard network traffic or activities that do not involve sending custom input directly to these two specific management ports.

Is my Cisco device at risk if it is not on the public internet?

Halo Surface Signal indicates that while devices reachable from the public internet are at highest risk, the danger remains for any switch where these ports are accessible. Even if a device is internal, any actor or compromised machine within your network segment can reach these ports if they are not explicitly blocked or firewalled, potentially leading to unauthorized root-level access.

What are the first steps to address this issue?

Begin by auditing your environment to identify all Cisco Nexus 9000 Series switches currently in use. Coordinate with your network and infrastructure teams to verify if TCP ports 43210 and 43211 are open or reachable in your configuration. Prioritize securing these ports against unauthorized access and monitor official security updates from the manufacturer to apply the necessary patches once available.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-s…

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.