CVE-2026-39671: WooCommerce Extra Fees Plugin CSRF Flaw

CVE-2026-39671 Overview

A Cross-Site Request Forgery (CSRF) vulnerability has been identified in the Dotstore Extra Fees Plugin for WooCommerce (woo-conditional-product-fees-for-checkout). This vulnerability allows attackers to trick authenticated administrators into performing unintended actions on the WordPress admin panel by crafting malicious requests that bypass CSRF protections.

Critical Impact

Attackers can exploit this CSRF vulnerability to manipulate fee configurations, modify checkout settings, or perform other administrative actions without authorization by deceiving authenticated administrators into clicking malicious links or visiting attacker-controlled pages.

Affected Products

• Extra Fees Plugin for WooCommerce versions through 4.3.3
• WordPress installations using the woo-conditional-product-fees-for-checkout plugin
• WooCommerce-based e-commerce sites with the vulnerable plugin installed

Discovery Timeline

• 2026-04-08 - CVE CVE-2026-39671 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2026-39671

Vulnerability Analysis

This Cross-Site Request Forgery (CSRF) vulnerability exists in the Extra Fees Plugin for WooCommerce due to missing or improper nonce verification on administrative actions. WordPress uses nonces (number used once) as security tokens to protect against CSRF attacks by ensuring that requests originate from legitimate sources within the WordPress admin interface.

The vulnerability affects all versions of the plugin up to and including 4.3.3. When exploited, an attacker can craft a malicious HTML page or link that, when visited by an authenticated administrator, will execute administrative actions on behalf of that user without their knowledge or consent.

Root Cause

The root cause of this vulnerability is the failure to implement proper CSRF protection mechanisms in the plugin's administrative functions. Specifically, the plugin does not adequately verify WordPress nonce tokens (wp_nonce_field, wp_verify_nonce) on form submissions or AJAX requests that modify plugin settings. This oversight allows attackers to forge requests that appear legitimate to the server since the session cookie is automatically included when the victim's browser makes the request.

Attack Vector

The attack vector involves social engineering combined with web-based exploitation:

1. Reconnaissance: The attacker identifies a WordPress site running the vulnerable Extra Fees Plugin for WooCommerce
2. Payload Crafting: The attacker creates a malicious web page containing hidden forms or JavaScript that automatically submits requests to the victim's WordPress admin panel
3. Social Engineering: The attacker tricks an authenticated WordPress administrator into visiting the malicious page (via phishing email, forum post, or embedded iframe)
4. Exploitation: When the administrator visits the page, their browser automatically sends the forged request along with their session cookies
5. Impact: The malicious action is executed with the administrator's privileges, potentially modifying fee structures, checkout behavior, or other plugin settings

Since no verified code examples are available, the exploitation mechanism relies on standard CSRF techniques where a hidden form auto-submits to the WordPress admin endpoint handling the plugin's configuration changes. The browser includes the victim's authentication cookies automatically, making the request appear legitimate to the server.

Detection Methods for CVE-2026-39671

Indicators of Compromise

• Unexpected changes to WooCommerce fee configurations without administrator action
• Audit logs showing administrative plugin actions occurring at unusual times or from unexpected IP addresses
• Modified checkout fee rules that were not intentionally configured by site administrators

Detection Strategies

• Review WordPress audit logs for modifications to the Extra Fees Plugin settings that coincide with administrator browsing sessions on external sites
• Monitor for unusual patterns in wp-admin requests to the woo-conditional-product-fees-for-checkout plugin endpoints
• Implement web application firewalls (WAF) with CSRF detection capabilities to identify suspicious cross-origin form submissions

Monitoring Recommendations

• Enable comprehensive logging for WordPress administrative actions, particularly plugin configuration changes
• Deploy SentinelOne Singularity to monitor endpoint activity and detect anomalous browser behavior patterns
• Regularly audit plugin settings to identify unauthorized modifications to fee structures

How to Mitigate CVE-2026-39671

Immediate Actions Required

• Update the Extra Fees Plugin for WooCommerce to a version newer than 4.3.3 when a patch becomes available
• Review and verify all current plugin configurations to ensure no unauthorized changes have been made
• Educate administrators about CSRF attacks and the importance of not clicking suspicious links while logged into WordPress

Patch Information

Organizations should monitor the Patchstack CSRF Vulnerability Advisory for updates on patch availability. The vendor is expected to release a security update that implements proper nonce verification for all administrative functions.

Workarounds

• Limit administrator access to the WordPress dashboard from trusted IP addresses only using .htaccess or server-level firewall rules
• Use browser extensions or separate browser profiles for WordPress administration to isolate session cookies
• Consider temporarily deactivating the plugin until a patched version is released if fee management functionality is not critical

# WordPress .htaccess restriction for wp-admin (workaround)
# Add to .htaccess in wp-admin directory
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.100$
    RewriteCond %{REMOTE_ADDR} !^10\.0\.0\.50$
    RewriteRule ^(.*)$ - [F,L]
</IfModule>