CVE-2026-7044: GreenCMS Unrestricted Upload RCE Flaw

CVE-2026-7044 Overview

A vulnerability has been identified in GreenCMS versions up to 2.3 that allows unrestricted file uploads through the themeadd function. The affected endpoint /index.php?m=admin&c=custom&a=themeadd fails to properly validate uploaded files, potentially enabling attackers to upload malicious content to the server. This vulnerability can be exploited remotely by authenticated users and the exploit details have been publicly disclosed. It is important to note that this vulnerability affects a product that is no longer supported by its maintainer.

Critical Impact
Unrestricted file upload vulnerability allows authenticated attackers to upload arbitrary files to the GreenCMS server, potentially leading to remote code execution or server compromise.

Affected Products

GreenCMS up to version 2.3

Discovery Timeline

2026-04-26 - CVE CVE-2026-7044 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7044

Vulnerability Analysis

This vulnerability exists within the theme addition functionality of GreenCMS, specifically in the themeadd function accessible through the admin custom controller. The flaw stems from improper access control (CWE-284) where the application fails to implement adequate restrictions on the types of files that can be uploaded during theme installation. An authenticated attacker with access to the admin panel can leverage this weakness to upload arbitrary files, including potentially executable scripts or web shells.

The vulnerability is exploitable over the network and requires low privileges to execute. While the impact on confidentiality, integrity, and availability is limited, the public availability of exploit information increases the risk of active exploitation.

Root Cause

The root cause of this vulnerability is improper access control in the file upload handling mechanism. The themeadd function in /index.php?m=admin&c=custom&a=themeadd does not enforce proper file type validation or restrictions, allowing users to bypass intended security controls and upload files of any type to the server.

Attack Vector

The attack vector is network-based, targeting the admin custom controller endpoint. An attacker with valid administrative credentials can access the theme addition functionality and exploit the unrestricted upload capability. The attack does not require user interaction beyond the initial authentication, and the exploit methodology has been publicly documented.

The vulnerability allows an authenticated user to navigate to the theme addition page at /index.php?m=admin&c=custom&a=themeadd and upload a malicious file disguised as a theme component. Due to the lack of file type validation, the server accepts and stores the file, which can then be executed or accessed depending on its nature and server configuration.

Detection Methods for CVE-2026-7044

Indicators of Compromise

Unexpected file uploads in GreenCMS theme directories
Presence of executable files (.php, .phtml, .phar) in theme upload locations
Unusual access patterns to the /index.php?m=admin&c=custom&a=themeadd endpoint
Web shells or backdoors appearing in the CMS file structure

Detection Strategies

Monitor HTTP POST requests to /index.php?m=admin&c=custom&a=themeadd for suspicious file uploads
Implement file integrity monitoring on GreenCMS installation directories
Review access logs for repeated or automated access to theme upload functionality
Deploy web application firewall rules to inspect uploaded file content

Monitoring Recommendations

Enable verbose logging for file upload operations in GreenCMS
Set up alerts for new file creation in theme directories with executable extensions
Monitor for unusual outbound connections from the web server that may indicate backdoor activity
Regularly audit admin user accounts and their access patterns

How to Mitigate CVE-2026-7044

Immediate Actions Required

Restrict access to the admin panel to trusted IP addresses only
Audit existing uploaded files for any malicious content
Consider disabling the theme upload functionality if not required
Review and remove any unauthorized admin accounts
Migrate to an actively maintained CMS solution as GreenCMS is no longer supported

Patch Information

No official patch is available as GreenCMS is no longer maintained by its developer. Organizations using this software should consider migrating to an alternative content management system that receives regular security updates. For reference, vulnerability details have been documented in the GitHub Issue Report and tracked in VulDB #359623.

Workarounds

Implement server-side file type validation through web server configuration
Use .htaccess or equivalent rules to prevent execution of uploaded files in theme directories
Deploy a web application firewall to filter malicious file uploads
Restrict admin panel access using network-level controls

bash

# Configuration example - Apache .htaccess to prevent script execution in upload directories
# Place in the GreenCMS theme upload directory

<FilesMatch "\.(php|phtml|php5|php7|phar|exe|sh|cgi)$">
    Order Deny,Allow
    Deny from all
</FilesMatch>

# Additionally, disable script execution
Options -ExecCGI
RemoveHandler .php .phtml .php5 .php7 .phar