CVE-2024-6313: Gutenberg Forms Plugin RCE Vulnerability

CVE-2024-6313 Overview

The Gutenberg Forms plugin for WordPress contains a critical arbitrary file upload vulnerability that allows unauthenticated attackers to upload malicious files to affected websites. The vulnerability exists in versions up to and including 2.2.9 due to improper handling of user-specified file type restrictions in the upload function. This flaw enables attackers to bypass intended security controls and upload arbitrary files, potentially leading to remote code execution on the affected server.

Critical Impact

Unauthenticated attackers can upload arbitrary files including PHP web shells, enabling complete server compromise and remote code execution without any authentication requirements.

Affected Products

• Gutenberg Forms WordPress Plugin versions up to and including 2.2.9
• WordPress installations with the vulnerable Gutenberg Forms plugin installed

Discovery Timeline

• 2024-07-09 - CVE CVE-2024-6313 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-6313

Vulnerability Analysis

This vulnerability represents a critical security flaw in the file upload handling mechanism of the Gutenberg Forms WordPress plugin. The core issue lies in the fact that users can specify their own allowed file types in the upload function, effectively bypassing any server-side restrictions intended to prevent dangerous file uploads.

The vulnerability is particularly severe because it requires no authentication to exploit. An unauthenticated attacker can leverage this flaw to upload PHP files or other executable scripts directly to the web server. Once uploaded, these malicious files can be accessed via HTTP requests, allowing the attacker to execute arbitrary code in the context of the web server.

The vulnerability exists within the Bucket.php utility file and the email.php trigger component, where file upload handling fails to properly sanitize and restrict file types regardless of user-supplied parameters. This design flaw means that even if administrators configure restrictions, attackers can override them.

Root Cause

The root cause of this vulnerability is improper input validation in the file upload functionality. The upload function in Utils/Bucket.php accepts user-controlled input for determining allowed file types without adequate server-side enforcement. This represents a fundamental violation of secure coding principles—specifically, trusting client-side or user-supplied data to enforce security controls.

The plugin fails to implement a server-side whitelist of safe file extensions that cannot be overridden by user input, allowing attackers to specify executable file types like .php, .phtml, or other web shell formats.

Attack Vector

The attack is conducted over the network without requiring any authentication or user interaction. An attacker can craft malicious HTTP requests to the vulnerable upload endpoint, specifying arbitrary file types to be allowed. The attack flow typically involves:

1. Identifying a WordPress site running a vulnerable version of Gutenberg Forms
2. Crafting a multipart form upload request with malicious payload
3. Manipulating the allowed file types parameter to include executable extensions
4. Uploading a PHP web shell or backdoor to the server
5. Accessing the uploaded file to execute arbitrary commands

The vulnerability in the file upload function allows attackers to manipulate the permitted file types through form parameters. By specifying dangerous extensions like .php in the allowed types, attackers can upload executable scripts that provide complete server access. Technical details about the specific vulnerable code paths can be found in the WordPress Plugin Code File and WordPress Plugin Email Trigger references.

Detection Methods for CVE-2024-6313

Indicators of Compromise

• Unexpected PHP files or scripts appearing in WordPress upload directories
• Web server logs showing POST requests to Gutenberg Forms upload endpoints with suspicious file extensions
• New or modified files in wp-content/uploads/ with executable extensions (.php, .phtml, .phar)
• Outbound network connections from the web server process to unknown destinations
• Presence of web shells or backdoors such as common patterns like eval(), base64_decode(), or system() functions

Detection Strategies

• Monitor file system changes in WordPress upload directories for new executable files
• Implement web application firewall (WAF) rules to block file uploads with dangerous extensions
• Review web server access logs for unusual POST requests to form submission endpoints
• Deploy file integrity monitoring to detect unauthorized modifications to the web root
• Utilize SentinelOne's Singularity Platform to detect and prevent web shell execution attempts

Monitoring Recommendations

• Enable detailed logging on WordPress file upload operations
• Configure alerts for new PHP files created in upload directories
• Monitor process execution from web server contexts (www-data, apache, nginx users)
• Implement regular vulnerability scanning to identify unpatched plugins
• Review web server error logs for signs of attempted exploitation

How to Mitigate CVE-2024-6313

Immediate Actions Required

• Update Gutenberg Forms plugin to a patched version immediately
• Audit WordPress upload directories for any suspicious or unexpected files
• Review web server access logs for signs of exploitation attempts
• Consider temporarily disabling the Gutenberg Forms plugin until patched
• Implement additional file upload restrictions at the web server level

Patch Information

Organizations using the Gutenberg Forms WordPress plugin should update to a version newer than 2.2.9 that addresses this vulnerability. The plugin can be updated through the WordPress admin dashboard under Plugins > Installed Plugins, or by downloading the latest version from the WordPress plugin repository.

For detailed vulnerability analysis and remediation guidance, refer to the Wordfence Vulnerability Analysis.

Workarounds

• Implement server-side file upload restrictions using .htaccess or web server configuration
• Use a Web Application Firewall (WAF) to block malicious file uploads
• Restrict file upload functionality to authenticated users only at the server level
• Disable the Gutenberg Forms plugin temporarily until an update can be applied
• Configure upload directories to prevent PHP execution

# Apache .htaccess configuration to prevent PHP execution in uploads
# Add this to your wp-content/uploads/.htaccess file
<FilesMatch "\.(?:php|phtml|php3|php4|php5|phar)$">
    Order Allow,Deny
    Deny from all
</FilesMatch>

# For Nginx, add to your server block:
# location ~* /wp-content/uploads/.*\.php$ {
#     deny all;
# }