CVE-2024-20399: Cisco NX-OS Command Injection Vulnerability

CVE-2024-20399 is a command injection vulnerability in the command line interface (CLI) of Cisco NX-OS. An authenticated local attacker who can reach the CLI may execute arbitrary commands as root on the underlying operating system of an affected device. Because NX-OS commonly runs on core network switches and fabric devices, successful abuse can give an attacker full control of the platform and a foothold for further lateral movement or traffic interception. Exact affected releases and configurations must be confirmed against the vendor advisory.

How it works

The flaw is classified as CWE-78 (OS Command Injection). In products of this class, user-supplied input that reaches a shell or system call is not sufficiently sanitized. On Cisco NX-OS the injection surface is the CLI itself. An attacker who already possesses valid local credentials can craft CLI input that causes the device to execute additional operating-system commands with root privileges. No remote unauthenticated path is described; the attacker must first obtain authenticated local access. Public detail beyond the CISA summary is limited, so defenders should treat any CLI session that can reach the vulnerable code path as potentially dangerous until the vendor patch is applied.

Am I affected? How to find it in your systems

Cisco NX-OS is the operating system used on many Cisco Nexus data-center switches, some MDS storage switches, and selected other Cisco networking platforms. Inventory every device that reports NX-OS as its OS. Typical discovery methods include:

• Network management platforms or configuration management databases that already track Cisco hardware and software versions.
• SNMP or CLI queries that return the software version string (for example, “show version”).
• Asset-scanning tools that fingerprint Cisco devices on management interfaces.

Compare the collected version strings against the fixed releases listed in the Cisco advisory for CVE-2024-20399. Also note any devices that allow local CLI access via console, SSH, or other management channels; those are the ones that expose the attack surface. Telemetry or logging signs of exploitation are not specifically documented, but look for unexpected CLI command sequences, sudden privilege escalations, or new processes running as root that do not match normal administrative activity. Confirm all version and configuration details against the official vendor advisory before declaring a device safe.

How to remediate

The primary remediation is to apply the software update published by Cisco for the affected NX-OS releases. Follow the vendor’s installation and verification procedures exactly; reboot or reload requirements, if any, will be stated in the advisory. After patching, re-inventory the devices to confirm the new version is running. For this class of vulnerability, additional hardening steps reduce residual risk:

• Enforce least-privilege CLI accounts so that only necessary administrators can reach the shell.
• Restrict management-plane access with ACLs, VRFs, or out-of-band management networks so that only trusted jump hosts can open CLI sessions.
• Enable and retain detailed CLI accounting and AAA logging so that any future injection attempts leave an audit trail.

If the vendor provides additional mitigations or configuration work-arounds, implement those as well. CISA’s required action is to apply the vendor mitigations or to discontinue use of the product if mitigations are unavailable.

If you can't patch immediately

Until the official update can be installed, reduce exposure with compensating controls that limit who can reach the CLI and what they can do:

• Segment management interfaces onto isolated networks reachable only from hardened jump hosts or bastion servers.
• Disable or tightly control any unused management protocols and remove unnecessary local accounts.
• Apply temporary access-control lists or firewall rules that allow CLI access solely from known administrative source addresses.
• Increase monitoring of authentication logs, CLI session starts, and process creation events for anomalous root-level activity.
• Where a web or API management plane exists, consider temporary virtual-patching rules that block suspicious command patterns, but treat this only as a short-term bridge; the root cause remains the unpatched CLI.

These measures do not eliminate the vulnerability; they only shrink the window of opportunity until the vendor patch is applied.

If your data may have been exposed

Actively exploited command-injection flaws on network infrastructure can lead to full device compromise and subsequent data exposure or lateral movement. Ransomware use of this specific CVE is not documented. If you suspect an affected device was abused, treat the incident as a potential breach: isolate the device, preserve logs, and begin forensic review. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether any related credentials have already appeared in public dumps.