CVE-2026-20212 in NX-OS Software
Summary
by MITRE • 09/02/2026
A vulnerability in the Silicon One integration for Cisco Nexus 9000 Series Switches could allow an unauthenticated, remote attacker to execute code with root privileges.
This vulnerability exists because TCP ports 43210 and 43211 are accessible in the default Layer 3 (L3) virtual routing and forwarding (VRF). A successful exploit could allow the attacker to connect to an affected device and send crafted input that could be executed as code with root privileges. The exploitation of this vulnerability could also cause the S1HAL process to crash, which could cause the device to reload.
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Analysis
by VulDB Data Team • 09/02/2026
The Cisco Nexus 9000 Series Switches incorporate a Silicon One integration designed to optimize packet processing and hardware acceleration through specialized silicon interfaces. Within this architecture, specific management or diagnostic services are exposed via TCP ports 43210 and 43211. These ports are accessible by default within the Layer 3 virtual routing and forwarding (VRF) context, which is a standard configuration for managing network traffic isolation and routing policies on enterprise-grade switches. The presence of these open ports in the default VRF creates an unintended attack surface that bypasses typical security boundaries intended to restrict access to critical management functions.
The core technical flaw lies in the lack of authentication mechanisms required to interact with services listening on these specific TCP ports. An unauthenticated, remote attacker who has network connectivity to the affected switch can establish a connection to port 43210 or 43211 and transmit specially crafted input data. Due to insufficient validation of this incoming data by the Silicon One integration software, the malformed packets are processed in a manner that allows arbitrary code execution. This flaw effectively grants the attacker the ability to execute commands with root privileges on the underlying operating system of the switch, representing a critical escalation from remote network access to full control over the device infrastructure.
The operational impact of exploiting this vulnerability is severe and multifaceted. Beyond the immediate risk of unauthorized command execution that could lead to complete compromise of the network switching fabric, the exploitation also poses significant stability risks. Specifically, triggering the flaw can cause the S1HAL process, which handles Silicon One hardware abstraction layer functions, to crash. This process failure results in a device reload or reboot, leading to a denial of service condition for all traffic passing through the affected switch. In high-availability environments, such an unexpected restart could disrupt network connectivity and trigger failover mechanisms that may themselves introduce temporary instability or configuration inconsistencies across the data center fabric.
From a classification perspective, this vulnerability aligns with CWE-287 Improper Authentication, as the system fails to verify the identity of users attempting to access critical resources. Furthermore, it relates to CWE-94 Code Injection, where untrusted input is executed in an unintended context due to insufficient sanitization or validation. In terms of adversary behavior mapping under MITRE ATT&CK, this vulnerability facilitates Initial Access via Remote Services and enables Privilege Escalation from a low-privilege network user to the system root level, allowing for subsequent lateral movement within the internal network segment protected by the switch.
To mitigate this risk, administrators should immediately restrict access to TCP ports 43210 and 43211 using Access Control Lists (ACLs) applied to the relevant VRF interfaces or physical management ports. These ACLs must be configured to permit traffic only from trusted management stations that require legitimate interaction with Silicon One services, effectively blocking all other sources including untrusted network segments. Additionally, ensuring that the switch firmware is updated to the latest version provided by Cisco is critical, as vendor patches typically address such integration flaws by either removing unnecessary service exposure or implementing proper authentication checks within the S1HAL process. Regular auditing of open ports and adherence to least-privilege principles for management plane access are essential practices to prevent similar exploitation vectors in network infrastructure devices.