A cross-site scripting (XSS) vulnerability has been discovered in OPNsense before 23.7.5, an open-source firewall and routing platform. This vulnerability involves the index.php sequence parameter on the Lobby Dashboard and allows an attacker to execute arbitrary JavaScript in the context of the user's browser. In this post, we'll be discussing the exploit details, examining a code snippet, and referencing original materials for further research and mitigation.

Exploit Details

CVE-2023-44276 refers to an XSS vulnerability present in OPNsense before version 23.7.5. The vulnerability is caused due to improper validation of user-supplied input in the "sequence parameter" of the index.php file, specifically when handling a request to the Lobby Dashboard. When exploited, this vulnerability allows an attacker to inject and execute arbitrary JavaScript, which can result in the theft of sensitive information, modification of displayed content, or any other actions performed by the user in the context of their browser session.

Here's a sample proof of concept (PoC) illustrating the vulnerability

*Payload:*

http://<target>/index.php?sequence=<script>alert('XSS')</script>;

If this payload is placed in the URL and the victim accesses the URL, an alert box with the message 'XSS' would pop up, indicating that a successful XSS attack has been executed.

Code Snippet

The vulnerability lies in the improper handling of the sequence parameter passed to the index.php page. Here's a code snippet demonstrating the part of the index.php file handling this user-supplied input:

<?php

// ... other code ...

// Handle the sequence parameter
$sequence = $_GET['sequence'];

if (!empty($sequence)) {
    // The user-supplied input is directly used without proper sanitization
    echo "<script>$sequence;</script>";
}

// ... other code ...

?>

As demonstrated in the code snippet above, the user-supplied input (the sequence parameter) is directly echoed onto the page without proper sanitization, thus allowing an attacker to inject arbitrary JavaScript code.

For further details on the vulnerability, consult the following authoritative sources

1. Official CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-44276

Mitigation Steps

In order to address the CVE-2023-44276 vulnerability, users of OPNsense should update their installation to version 23.7.5 or later. The updated version includes a fix for the problem, which ensures proper input validation and sanitization, thereby eliminating the possibility of a successful XSS attack.

Furthermore, users should always practice caution when clicking on links sent by unknown sources and be wary of unusual behavior on the platform that may indicate the presence of an exploit.

In conclusion, the CVE-2023-44276 vulnerability highlights the importance of proper input validation and the potential risks posed by XSS vulnerabilities. While this vulnerability has been addressed in version 23.7.5 of OPNsense, users should still remain vigilant and keep their software updated to protect themselves from future vulnerabilities.

Timeline

Published on: 09/28/2023 05:15:00 UTC
Last modified on: 10/02/2023 19:04:00 UTC