CVE-2025-27355: WooCommerce Loi Hamon CSRF Vulnerability

CVE-2025-27355 Overview

CVE-2025-27355 is a Cross-Site Request Forgery (CSRF) vulnerability in the Woocommerce – Loi Hamon WordPress plugin developed by Nicolas GRILLET. This vulnerability allows attackers to chain CSRF with Stored Cross-Site Scripting (XSS), enabling malicious actors to inject persistent scripts into the affected WordPress installation by exploiting the lack of proper CSRF token validation.

Critical Impact

Attackers can leverage this CSRF vulnerability to inject stored XSS payloads, potentially compromising administrator sessions, defacing websites, or stealing sensitive user data from affected WooCommerce installations.

Affected Products

• Woocommerce – Loi Hamon plugin versions up to and including 1.1.0
• WordPress installations running the vulnerable plugin versions
• WooCommerce-based e-commerce sites using the Loi Hamon compliance plugin

Discovery Timeline

• 2025-02-24 - CVE-2025-27355 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-27355

Vulnerability Analysis

This vulnerability combines two distinct attack vectors: Cross-Site Request Forgery (CSRF) and Stored Cross-Site Scripting (XSS). The Woocommerce – Loi Hamon plugin, which is designed to help WooCommerce stores comply with French "Loi Hamon" consumer protection regulations, fails to implement proper CSRF protections on its administrative endpoints. This lack of validation allows attackers to craft malicious requests that, when executed by an authenticated administrator, inject persistent XSS payloads into the plugin's stored settings or content areas.

The chained nature of this vulnerability (CSRF-to-Stored-XSS) makes it particularly dangerous. The CSRF component bypasses origin validation, while the Stored XSS component ensures that malicious scripts persist across page loads, affecting all users who view the compromised content.

Root Cause

The root cause of this vulnerability is the absence of CSRF token validation (nonce verification in WordPress terminology) on form submissions or AJAX endpoints within the plugin's administrative interface. WordPress provides built-in functions like wp_nonce_field() and wp_verify_nonce() for CSRF protection, but these were not properly implemented in the affected plugin versions. Additionally, user-supplied input is stored without adequate sanitization or encoding, enabling the Stored XSS component of the attack chain.

Attack Vector

The attack requires social engineering to trick an authenticated WordPress administrator into visiting a malicious webpage or clicking a crafted link. The attacker's page contains a hidden form or JavaScript that automatically submits a request to the vulnerable plugin endpoint. Since the administrator's browser automatically includes authentication cookies, the malicious request is processed as if the administrator intentionally submitted it. The payload containing XSS scripts is then stored in the database and executed whenever users access the affected pages.

The exploitation flow typically involves:

1. Attacker crafts a malicious HTML page with an auto-submitting form targeting the vulnerable endpoint
2. Victim administrator is lured to visit the attacker's page while logged into WordPress
3. The form submits a request containing XSS payload to the plugin's unprotected endpoint
4. The XSS payload is stored in the WordPress database
5. The stored script executes whenever users view the affected content

Detection Methods for CVE-2025-27355

Indicators of Compromise

• Unexpected JavaScript code or <script> tags in plugin settings or database entries related to Loi Hamon functionality
• Suspicious administrative activity logs showing settings changes without corresponding admin sessions
• Browser console errors or unexpected script execution on WooCommerce pages
• Reports of session hijacking or unauthorized administrative access

Detection Strategies

• Review WordPress database tables associated with the Loi Hamon plugin for embedded script tags or event handlers
• Monitor HTTP access logs for unusual POST requests to Loi Hamon plugin endpoints from external referrers
• Implement Content Security Policy (CSP) headers to detect and block unauthorized inline script execution
• Use WordPress security plugins to scan for stored XSS payloads in the database

Monitoring Recommendations

• Enable detailed WordPress audit logging for plugin configuration changes
• Configure Web Application Firewall (WAF) rules to detect CSRF attack patterns and XSS payloads
• Implement real-time alerting for administrative setting modifications outside of normal maintenance windows

How to Mitigate CVE-2025-27355

Immediate Actions Required

• Immediately review the Loi Hamon plugin settings for any unauthorized modifications or suspicious content
• Consider temporarily deactivating the Woocommerce – Loi Hamon plugin until a patched version is available
• Audit WordPress database entries for stored XSS payloads and sanitize any discovered malicious content
• Educate administrators about the risks of clicking unknown links while logged into WordPress

Patch Information

As of the data available, versions through 1.1.0 are affected. Administrators should monitor the WordPress plugin repository and the Patchstack Vulnerability Report for updates from the plugin developer. When a patched version becomes available, update immediately through the WordPress admin dashboard.

Workarounds

• Deactivate the Woocommerce – Loi Hamon plugin until a security patch is released
• Implement additional security headers including strict Content-Security-Policy to mitigate XSS impact
• Use WordPress security plugins that add CSRF protection layers to administrative endpoints
• Restrict administrative access to trusted IP addresses only

# WordPress .htaccess configuration to restrict wp-admin access
# Add to .htaccess in /wp-admin/ directory

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/wp-admin/
RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.100$
RewriteRule ^(.*)$ - [F,L]
</IfModule>

# Add CSP headers in main .htaccess
<IfModule mod_headers.c>
Header set Content-Security-Policy "script-src 'self'; object-src 'none';"
Header set X-Content-Type-Options "nosniff"
Header set X-XSS-Protection "1; mode=block"
</IfModule>