CVE-2026-7043: GreenCMS Unrestricted Upload RCE Vulnerability

CVE-2026-7043 Overview

A vulnerability has been identified in GreenCMS versions up to 2.3 that allows unrestricted file upload through the pluginAddLocal function. This vulnerability is accessible via the file /index.php?m=admin&c=custom&a=pluginadd and can be exploited remotely by authenticated attackers. The exploit has been publicly disclosed, and it's important to note that this vulnerability affects products that are no longer supported by the maintainer.

Critical Impact
Unrestricted file upload vulnerabilities can allow attackers to upload malicious files such as web shells, potentially leading to remote code execution, data exfiltration, and complete system compromise.

Affected Products

GreenCMS up to version 2.3
Specifically affects the plugin upload functionality at /index.php?m=admin&c=custom&a=pluginadd
Products no longer supported by the maintainer

Discovery Timeline

2026-04-26 - CVE-2026-7043 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7043

Vulnerability Analysis

This vulnerability affects the pluginAddLocal function in GreenCMS, which handles plugin uploads through the administrative interface. The core issue is classified under CWE-284 (Improper Access Control), indicating that the application fails to properly restrict what types of files can be uploaded through this functionality.

The unrestricted upload vulnerability allows an authenticated attacker with access to the admin panel to upload arbitrary files without proper validation of file type, content, or extension. This lack of validation can be leveraged to upload executable files such as PHP web shells, which can then be accessed to execute arbitrary commands on the underlying server.

Since GreenCMS is no longer maintained, this vulnerability will not receive an official patch from the original developers, making it particularly dangerous for any installations still in active use.

Root Cause

The root cause of this vulnerability lies in the pluginAddLocal function's failure to implement proper file validation mechanisms. The function does not adequately check:

File extensions against an allowlist of safe file types
MIME type validation to ensure uploaded content matches expected formats
File content inspection to detect potentially malicious payloads

This improper access control (CWE-284) allows attackers to bypass any intended restrictions on file uploads, enabling them to place arbitrary files on the server.

Attack Vector

The attack is initiated remotely over the network and requires low-privilege authentication to the administrative interface. An attacker would:

Authenticate to the GreenCMS admin panel
Navigate to the plugin upload functionality at /index.php?m=admin&c=custom&a=pluginadd
Upload a malicious file disguised as a legitimate plugin
Access the uploaded file directly to execute malicious code

The vulnerability is exploited through the manipulation of the file upload functionality, where the pluginAddLocal function accepts files without proper validation. Technical details and proof of concept information can be found in the GitHub Issue Discussion and VulDB entry.

Detection Methods for CVE-2026-7043

Indicators of Compromise

Unexpected files appearing in plugin directories, particularly PHP files with suspicious names or obfuscated code
Unusual HTTP POST requests to /index.php?m=admin&c=custom&a=pluginadd from external IP addresses
Web shell signatures or backdoor files in the GreenCMS installation directory
Anomalous outbound connections from the web server

Detection Strategies

Monitor web server access logs for requests to the vulnerable endpoint /index.php?m=admin&c=custom&a=pluginadd
Implement file integrity monitoring on the GreenCMS installation directory to detect unauthorized file additions
Deploy web application firewall (WAF) rules to inspect file upload requests for malicious content
Use YARA rules or signature-based scanning to detect common web shell patterns in uploaded files

Monitoring Recommendations

Enable detailed logging for all administrative actions within GreenCMS
Set up alerts for file system changes in the plugin directories
Monitor for execution of newly created files in web-accessible directories
Review authentication logs for unauthorized access attempts to the admin panel

How to Mitigate CVE-2026-7043

Immediate Actions Required

Consider migrating away from GreenCMS since it is no longer maintained and will not receive security patches
Restrict access to the administrative interface using IP allowlisting or VPN requirements
Disable the plugin upload functionality if not required for operations
Implement strict file upload validation at the web server or WAF level

Patch Information

This vulnerability affects GreenCMS, which is no longer supported by the maintainer. No official security patch is available or expected. Organizations using GreenCMS should prioritize migration to an actively maintained CMS platform.

For additional technical details, refer to the VulDB entry and the GitHub Issue Discussion.

Workarounds

Implement web application firewall rules to block or inspect requests to the vulnerable endpoint
Add server-side validation to restrict file uploads to specific safe extensions (e.g., .zip only for plugins)
Use .htaccess or equivalent configuration to prevent execution of uploaded files
Restrict admin panel access to trusted IP addresses only

bash

# Example: Apache .htaccess to prevent PHP execution in upload directories
<Directory "/path/to/greencms/plugins/">
    php_flag engine off
    <FilesMatch "\.php$">
        Deny from all
    </FilesMatch>
</Directory>