CVE-2025-39557: Kadence WooCommerce Email Designer RCE

CVE-2025-39557 Overview

CVE-2025-39557 is an unrestricted file upload vulnerability affecting the Kadence WooCommerce Email Designer plugin by StellarWP. This vulnerability allows attackers to upload files with dangerous types, specifically enabling the upload of web shells to web servers running vulnerable versions of the plugin. The flaw stems from CWE-434 (Unrestricted Upload of File with Dangerous Type), a critical class of vulnerability that can lead to complete server compromise.

Critical Impact

Successful exploitation allows attackers to upload malicious web shells, potentially leading to complete server takeover, data theft, and lateral movement within the hosting environment.

Affected Products

• Kadence WooCommerce Email Designer plugin versions up to and including 1.5.14
• WordPress sites running vulnerable versions of the kadence-woocommerce-email-designer plugin
• WooCommerce-enabled WordPress installations using the affected plugin

Discovery Timeline

• April 16, 2025 - CVE-2025-39557 published to NVD
• April 1, 2026 - Last updated in NVD database

Technical Details for CVE-2025-39557

Vulnerability Analysis

This vulnerability falls under the category of Unrestricted Upload of File with Dangerous Type (CWE-434). The Kadence WooCommerce Email Designer plugin fails to properly validate or restrict the types of files that can be uploaded through its functionality. This allows malicious actors to bypass intended security restrictions and upload executable files, including PHP web shells, directly to the web server.

Web shell upload vulnerabilities are particularly dangerous in WordPress environments because successful exploitation grants attackers persistent remote access to the server. Once a web shell is deployed, attackers can execute arbitrary commands, access sensitive database credentials, steal customer data, inject malicious code into legitimate site files, and use the compromised server as a pivot point for further attacks.

Root Cause

The root cause of this vulnerability lies in insufficient file type validation within the plugin's upload handling functionality. The affected versions of Kadence WooCommerce Email Designer do not properly verify that uploaded files conform to safe, expected file types. This lack of server-side validation allows attackers to craft requests that bypass any client-side restrictions and upload executable PHP files or other dangerous file types directly to accessible locations on the server.

Attack Vector

The attack vector involves exploiting the plugin's file upload mechanism to place a malicious PHP web shell on the target WordPress server. An attacker would typically:

1. Identify a WordPress site running a vulnerable version of Kadence WooCommerce Email Designer (<= 1.5.14)
2. Craft a malicious request to the plugin's upload endpoint, containing a PHP web shell disguised or directly uploaded
3. Bypass inadequate file type validation to successfully upload the malicious file
4. Access the uploaded web shell through a direct URL to gain remote command execution capabilities

The vulnerability may require some level of authentication depending on the specific implementation, but once exploited, it provides attackers with full server-side code execution capabilities.

Detection Methods for CVE-2025-39557

Indicators of Compromise

• Unexpected PHP files appearing in WordPress upload directories or plugin folders
• Web server access logs showing requests to unusual PHP files not part of legitimate WordPress installation
• Suspicious POST requests to Kadence WooCommerce Email Designer plugin endpoints containing file upload data
• New or modified files with recent timestamps in the wp-content/plugins/kadence-woocommerce-email-designer/ directory

Detection Strategies

• Monitor file system integrity for unexpected PHP file creation in WordPress directories
• Implement web application firewall (WAF) rules to detect and block web shell upload attempts
• Review Apache/Nginx access logs for POST requests to plugin upload endpoints followed by GET requests to unusual file paths
• Deploy endpoint detection solutions capable of identifying web shell behavior patterns

Monitoring Recommendations

• Enable file integrity monitoring (FIM) on all WordPress installation directories
• Configure alerting for any new PHP file creation outside of authorized deployment windows
• Monitor outbound network connections from the web server for suspicious command-and-control traffic
• Implement real-time log analysis for plugin-related upload activity

How to Mitigate CVE-2025-39557

Immediate Actions Required

• Update Kadence WooCommerce Email Designer to the latest patched version immediately
• Audit WordPress upload directories for any suspicious or unexpected PHP files
• Review web server access logs for evidence of exploitation attempts
• Temporarily disable the plugin if an update is not yet available and the functionality is not critical

Patch Information

Site administrators should update the Kadence WooCommerce Email Designer plugin to the latest available version that addresses this vulnerability. For detailed patch information and version guidance, refer to the Patchstack Vulnerability Report.

Workarounds

• Implement server-level file upload restrictions to block executable file types
• Use a web application firewall (WAF) with rules to detect and block web shell signatures
• Restrict write permissions on WordPress directories where possible
• Consider disabling file upload functionality through server configuration if the feature is not required

# Configuration example - Apache .htaccess to restrict PHP execution in uploads
# Add to wp-content/uploads/.htaccess
<Files "*.php">
    Require all denied
</Files>

# Alternative for Nginx - Add to server block
location ~* /wp-content/uploads/.*\.php$ {
    deny all;
}