Cisco Nexus Vulnerability Allows Attackers to Inject Malicious Commands

Cisco Systems has issued a critical security advisory for a newly disclosed command injection vulnerability affecting its Nexus 3000 and 9000 Series Switches operating in standalone NX-OS mode.

Tracked as CVE-2025-20161 (CVSSv3 score: 5.1), the flaw enables authenticated attackers with administrative privileges to execute arbitrary operating system commands with root-level permissions during software upgrade procedures.

The vulnerability, discovered internally by Cisco’s security teams, stems from inadequate validation mechanisms for specific software image components, allowing malicious actors to embed unauthorized commands into tampered firmware packages.

Technical Breakdown and Exploit Dynamics

The vulnerability exists in the image verification subsystem of Cisco NX-OS versions before 15.2(9)E1 for Nexus 3000 switches and 10.4(3a)F for Nexus 9000 devices.

Attackers exploiting this flaw must first obtain valid administrator credentials and physical/logical access to the targeted switch’s management interface.

By distributing a specially crafted software image containing hidden command sequences—disguised within metadata fields or checksum blocks—an attacker can bypass signature validation checks and trigger the execution of malicious payloads during the firmware installation process.

While the attack complexity remains relatively high due to the prerequisite administrative access, successful exploitation grants full control over the switch’s Linux-based underpinnings.

This could facilitate network reconnaissance, traffic interception, lateral movement, or persistent backdoor deployments across connected infrastructure.

Cisco’s advisory emphasizes that attackers could leverage this flaw to manipulate routing tables, intercept encrypted traffic flows, or disrupt network segmentation policies without triggering standard intrusion detection mechanisms.

Affected Products and Mitigation Strategies

The confirmed impacted devices include:

• Nexus 3000 Series Switches (all models running standalone NX-OS)
• Nexus 9000 Series Switches (standalone NX-OS deployments only)

Cisco explicitly excludes Nexus 9000 switches operating in Application-Centric Infrastructure (ACI) mode, MDS 9000 storage switches, and the entire Firepower appliance lineup from this vulnerability.

Organizations utilizing Nexus 5500/5600/6000/7000 hardware or UCS fabric interconnects remain unaffected.

As no viable workarounds exist, Cisco mandates the immediate installation of patched firmware versions:

• Nexus 3000 Series: Upgrade to NX-OS 15.2(9)E1 or newer
• Nexus 9000 Series: Migrate to NX-OS 10.4(3a)F or subsequent releases

Network administrators must utilize the Cisco Software Checker portal to verify their device’s vulnerability status and download cryptographically signed software bundles.

The company further advises enterprises to implement strict firmware provenance controls—including multi-party SHA-256 hash verification before deploying updates—and restrict administrative access to switch management interfaces using role-based access controls (RBAC).

Cisco’s Product Security Incident Response Team (PSIRT) confirms no active exploitation incidents have been observed but urges accelerated patch deployment cycles.

For organizations unable to immediately upgrade, network segmentation and continuous monitoring for unexpected configuration changes or unauthorized CLI command activity remain essential compensatory controls.

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