Catchy Introduction: The Contact Form 7 is a widely used WordPress plugin for managing contact forms on numerous websites. Unfortunately, the plugin is also known for vulnerabilities that attract hackers. On that note, this blog post focuses on the open redirect vulnerability found in Contact Form 7 WordPress plugin before 5.9.5, specifically CVE-2024-4704. Throughout this post, I will dive deep into the vulnerability, provide code snippets, links to references, and exploit details to help you understand the risks associated with the vulnerability and how you can address it.

Background: As a well-known plugin used by millions of websites, it is critical for developers and WordPress site administrators to be aware of the potential security risks which come with it. The open redirect vulnerability, identified as CVE-2024-4704, was discovered and fixed in version 5.9.5. An attacker can exploit this vulnerability by crafting a false URL that redirects users to a malicious website. This redirection can cause users to reveal sensitive information and credentials or become victims of phishing attacks. It is important to note that this vulnerability affects Contact Form 7 WordPress plugin versions before 5.9.5.

Detailed Vulnerability Description: The open redirect vulnerability is caused by improper validation of user-supplied input, particularly the _wp_http_referer parameter used in the HTTP response. This parameter can be manipulated by an attacker to construct a URL that leads unsuspecting users to a different website, potentially resulting in harm. The following code snippet shows the vulnerable section of the code in the includes/controller.php file:

// example code snippet from includes/controller.php
function wpcf7_submit_handler() {
    ...
    if (!empty($form->redirect_uri)) {
        $status = '')
        $url = esc_url_raw($form->redirect_uri);
        if (!empty($_REQUEST['_wp_http_referer'])) {
            $url = add_query_arg(
                '_wp_http_referer',
                urlencode(wp_unslash($_REQUEST['_wp_http_referer'])),
                $url
            );
        }

        $url = wpcf7_apply_filters('wpcf7_redirect_uri', $url, $form);
        wp_safe_redirect(esc_url_raw($url), 302, 'WPCF7');
        exit();
    }
    ...
}

Exploit Details: To exploit this vulnerability, an attacker can craft a false URL containing the malicious website link as the _wp_http_referer parameter value. When a user clicks on the crafted URL, the _wp_http_referer parameter is processed by the Contact Form 7 plugin, resulting in the redirection to the attacker's website. Here is a sample URL that demonstrates this exploit:

// example exploit URL
http://vulnerable_site.com/contact-form?_wp_http_referer=http://malicious_site.com

To mitigate this vulnerability, the site administrators should immediately update their Contact Form 7 plugin to version 5.9.5 or newer. This is because the developers of the plugin have already fixed the vulnerability in these later versions.

1. Contact Form 7 Changelog - 5.9.5 Update Details
2. CVE-2024-4704 NVD Information
3. WPScan Vulnerability Database - Contact Form 7 Open Redirect

Conclusion: Open redirect vulnerabilities like CVE-2024-4704 pose a serious threat to both website users and administrators. By staying informed about such vulnerabilities and updating the Contact Form 7 plugin whenever necessary, one can safeguard their WordPress site from potential exploitation. Stay safe out there!

Timeline

Published on: 06/27/2024 06:15:14 UTC
Last modified on: 07/03/2024 02:07:57 UTC