CVE-2023-20050: Cisco NX-OS Software RCE Vulnerability

CVE-2023-20050 Overview

A command injection vulnerability exists in the Command Line Interface (CLI) of Cisco NX-OS Software that allows an authenticated, local attacker to execute arbitrary commands on the underlying operating system of affected devices. This vulnerability stems from insufficient validation of arguments passed to specific CLI commands, enabling attackers to inject malicious input that gets executed with the privileges of the currently logged-in user.

Critical Impact

Authenticated attackers with local access can execute arbitrary operating system commands, potentially leading to complete device compromise, lateral movement within data center networks, and disruption of critical network infrastructure.

Affected Products

• Cisco NX-OS Software (multiple versions)
• Cisco MDS 9000 Series Multilayer Switches (MDS 9100, 9132T, 9134, 9140, 9148 series, 9200 series, 9500 series, 9700 series)
• Cisco Nexus 1000 Virtual Edge and Nexus 1000V
• Cisco Nexus 3000 Series Switches (3016, 3048, 3064 series, 3100 series, 3132 series, 3172 series, 3200 series, 3400 series, 3500 series, 3600 series)
• Cisco Nexus 5000 Series Switches (5500, 5548, 5596, 5600, 5624, 5648, 5672, 5696)
• Cisco Nexus 6000 Series Switches (6001, 6004)
• Cisco Nexus 7000 Series Switches (7004, 7009, 7010, 7018, 7700 series)
• Cisco Nexus 9000 Series Switches (standalone NX-OS mode)

Discovery Timeline

• February 23, 2023 - CVE-2023-20050 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20050

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw exists because the NX-OS CLI fails to properly sanitize and validate user-supplied input when processing arguments for certain CLI commands.

When an authenticated user executes specific CLI commands with crafted arguments, the underlying system does not adequately filter shell metacharacters or escape sequences. This allows an attacker to break out of the intended command context and inject additional operating system commands that execute with the same privilege level as the authenticated user session.

The attack requires local authentication to the device, meaning the attacker must have valid credentials and either console access or remote CLI access (SSH/Telnet) to the affected device. While this prerequisite reduces the attack surface compared to unauthenticated remote vulnerabilities, it remains a significant risk in environments where multiple administrators have device access or where credentials may have been compromised.

Root Cause

The root cause is insufficient input validation in the argument parsing logic for specific NX-OS CLI commands. The software fails to properly sanitize special characters and shell metacharacters (such as ;, |, &&, $(), backticks) that can be used to chain or embed additional commands. This allows user-controlled data to be interpreted as part of the command execution flow rather than as pure data arguments.

Attack Vector

The attack vector requires local access to an affected device with valid authentication credentials. An attacker would:

1. Authenticate to the affected NX-OS device through console, SSH, or other CLI access methods
2. Identify vulnerable CLI commands that accept user-supplied arguments
3. Craft malicious input containing OS command injection payloads
4. Execute the vulnerable command with the crafted payload as an argument
5. The injected commands execute on the underlying Linux-based operating system with the privileges of the current user session

Successful exploitation could allow attackers to read sensitive configuration data, modify device settings, establish persistent access, pivot to other network devices, or cause denial of service conditions.

Detection Methods for CVE-2023-20050

Indicators of Compromise

• Unusual CLI command history entries containing shell metacharacters (;, |, &&, $(), backticks) in command arguments
• Unexpected processes spawned from CLI sessions that are not typical NX-OS system processes
• Anomalous system log entries indicating command execution failures or unusual shell activity
• Evidence of unauthorized file access or modification on the underlying filesystem

Detection Strategies

• Enable comprehensive CLI accounting and audit logging on all NX-OS devices to capture detailed command execution history
• Implement centralized syslog collection and review for anomalous CLI activity patterns
• Deploy network behavior analysis tools to detect unusual management plane traffic to affected switches
• Establish baseline CLI usage patterns for each administrative user and alert on deviations

Monitoring Recommendations

• Configure AAA accounting to log all CLI commands executed on affected devices
• Monitor authentication logs for signs of credential compromise or brute-force attempts
• Implement real-time alerting for CLI commands containing suspicious characters or patterns
• Regularly review user access privileges and remove unnecessary accounts from network devices

How to Mitigate CVE-2023-20050

Immediate Actions Required

• Review the Cisco Security Advisory to identify affected software versions and obtain patched releases
• Inventory all Cisco MDS and Nexus switches in your environment running NX-OS software
• Restrict CLI access to only necessary administrative personnel using role-based access control (RBAC)
• Implement strong authentication mechanisms and regularly rotate administrative credentials

Patch Information

Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory to determine the appropriate fixed software release for their specific hardware platform and current NX-OS version. The advisory provides detailed version mapping for each affected product family, including MDS 9000 Series, Nexus 3000/5000/6000/7000/9000 Series, and Nexus 1000V/1000 Virtual Edge platforms.

Workarounds

• Limit CLI access to trusted administrators only and enforce least-privilege principles for all user accounts
• Implement out-of-band management networks to isolate device management traffic from production data paths
• Enable SSH key-based authentication and disable password-based CLI access where possible
• Deploy privileged access management (PAM) solutions to monitor and control administrative sessions

# Example: Restrict CLI access via RBAC configuration
# Configure role-based access control to limit command access
switch# configure terminal
switch(config)# role name network-operator
switch(config-role)# description Read-only network operator role
switch(config-role)# rule 1 permit read
switch(config-role)# rule 2 deny command configure *
switch(config-role)# exit

# Enable CLI command accounting
switch(config)# aaa accounting commands all default start-stop group tacacs+
switch(config)# logging level aaa 6