Security researchers have discovered a critical cross-site scripting (XSS) vulnerability (CVE-2023-39002) in the OPNsense open source firewall system. The security flaw exists in the act parameter of the system_certmanager.php file in OPNsense versions before 23.7. Attackers can exploit this vulnerability to execute arbitrary web scripts or HTML code via a carefully crafted payload. In this post, we will take a closer look at the vulnerability and explain its impact, how it can be exploited, and what you should do to protect your systems.

Description of Vulnerability

The OPNsense firewall system is designed to provide advanced security features for businesses and individuals alike. However, the recently reported XSS vulnerability can potentially allow an attacker to execute malicious code remotely and compromise a targeted computer's security.

The vulnerability exists in the act parameter of the system_certmanager.php file in OPNsense versions before 23.7. By injecting specially crafted web scripts or HTML code into the act parameter, a hacker could potentially execute arbitrary code remotely on a targeted system.

Here's a simple example of how the vulnerability might potentially be exploited<script>alert('XSS')</script>;

In this example, the injected script will simply display an alert box with the text 'XSS'. However, a more advanced attacker could potentially use this technique to execute more sophisticated code, steal sensitive information, or even compromise the security of the targeted system.

Exploit Details

The exploit essentially takes advantage of the fact that the act parameter is not properly sanitized before being passed to the web browser. This allows an attacker to inject malicious scripts, which will then be executed when the page is loaded in the victim's browser.

The following resources provide detailed information about the CVE-2023-39002 vulnerability

1. CVE Details:

Mitigation and Recommendations

Users of OPNsense should upgrade their systems immediately to the latest version (23.7 or later) to ensure that their systems are protected from this vulnerability. Additionally, it's essential to follow security best practices for mitigating XSS attacks, such as input validation, output encoding, and secure coding practices.

Use secure coding practices to avoid introducing vulnerabilities during development.


The CVE-2023-39002 vulnerability in the OPNsense firewall system demonstrates the importance of taking a proactive approach to security. By keeping your systems updated and following best practices for web application security, you stand the best chance of protecting your systems from XSS attacks and other security threats. Don't forget to upgrade your OPNsense installation to version 23.7 or later, to protect against this particular vulnerability.


Published on: 08/09/2023 19:15:00 UTC
Last modified on: 08/15/2023 15:07:00 UTC