CVE-2024-37555: Contact Form 7 PDF File Upload Vulnerability

CVE-2024-37555 Overview

CVE-2024-37555 is an Unrestricted Upload of File with Dangerous Type vulnerability affecting the ZealousWeb Generate PDF using Contact Form 7 WordPress plugin. This vulnerability allows attackers to upload arbitrary files with dangerous types to vulnerable WordPress installations, potentially leading to remote code execution and complete site compromise.

Critical Impact

This unrestricted file upload vulnerability can be exploited by unauthenticated remote attackers to upload malicious files, potentially resulting in full server compromise, data theft, and website defacement.

Affected Products

• ZealousWeb Generate PDF using Contact Form 7 versions up to and including 4.1.2
• WordPress installations with the vulnerable plugin active
• Web servers hosting affected WordPress sites

Discovery Timeline

• 2024-07-09 - CVE-2024-37555 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2024-37555

Vulnerability Analysis

This vulnerability falls under CWE-434 (Unrestricted Upload of File with Dangerous Type), which occurs when a web application allows users to upload files without proper validation of the file type or content. In the context of the Generate PDF using Contact Form 7 plugin, the file upload functionality fails to adequately restrict the types of files that can be uploaded through the contact form integration.

The plugin's purpose is to generate PDF documents from Contact Form 7 submissions, but the vulnerability exists in how the plugin handles file uploads during this process. Without proper file type validation, an attacker can bypass intended restrictions and upload executable files such as PHP web shells.

Root Cause

The root cause of CVE-2024-37555 is insufficient input validation on file uploads within the plugin. The vulnerable code path does not implement proper checks to verify that uploaded files match expected safe file types (such as images or documents). This oversight allows attackers to upload files with executable extensions like .php, .phtml, or other server-side script extensions that can be executed by the web server.

Key contributing factors include:

• Lack of server-side file type validation based on file content (magic bytes)
• Missing or inadequate file extension whitelisting
• Insufficient MIME type verification
• Potential bypass of any client-side validation mechanisms

Attack Vector

The attack vector for this vulnerability is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability remotely by:

1. Identifying a WordPress site running the vulnerable Generate PDF using Contact Form 7 plugin
2. Crafting a malicious request to the file upload endpoint
3. Uploading a PHP web shell or other malicious executable file
4. Accessing the uploaded file directly to execute arbitrary code on the server

The vulnerability enables attackers to upload malicious files such as PHP web shells. Once uploaded, these files can be accessed directly through the web server, allowing the attacker to execute arbitrary commands with the privileges of the web server user. This can lead to complete server compromise, data exfiltration, and lateral movement within the network.

For detailed technical analysis, see the Patchstack Vulnerability Report.

Detection Methods for CVE-2024-37555

Indicators of Compromise

• Presence of unexpected PHP files in the WordPress uploads directory or plugin directories
• Web shell files with common naming patterns (e.g., shell.php, c99.php, r57.php)
• Unusual POST requests to Contact Form 7 endpoints containing file upload payloads
• New or modified files with executable extensions in web-accessible directories

Detection Strategies

• Monitor file system changes in WordPress upload directories for newly created PHP or executable files
• Implement web application firewall (WAF) rules to detect and block malicious file upload attempts
• Review web server access logs for suspicious requests to uploaded file paths
• Use file integrity monitoring to alert on unexpected file changes within the WordPress installation

Monitoring Recommendations

• Enable detailed logging for Contact Form 7 submissions and file upload activities
• Configure alerts for any PHP file creation in upload directories
• Monitor outbound connections from the web server for signs of web shell communication
• Implement regular security scans of the WordPress file system

How to Mitigate CVE-2024-37555

Immediate Actions Required

• Update the Generate PDF using Contact Form 7 plugin to the latest patched version immediately
• Audit existing uploaded files for any suspicious or unexpected file types
• Remove any unauthorized PHP files from upload directories
• Temporarily disable the plugin if immediate patching is not possible

Patch Information

Organizations should update the ZealousWeb Generate PDF using Contact Form 7 plugin to a version newer than 4.1.2. Check the official WordPress plugin repository or the Patchstack vulnerability database for the latest security updates and patch availability.

Workarounds

• Implement server-side file type restrictions through web server configuration (Apache/Nginx)
• Disable PHP execution in upload directories by adding appropriate .htaccess rules
• Use a Web Application Firewall (WAF) to block malicious file upload attempts
• Restrict plugin access to authenticated users only if possible

# Apache .htaccess configuration to prevent PHP execution in uploads directory
# Add this to wp-content/uploads/.htaccess

<FilesMatch "\.(?:php|phtml|php3|php4|php5|phps)$">
    Require all denied
</FilesMatch>

# Alternatively, disable all script execution
<Files *.php>
    deny from all
</Files>