CVE-2021-41402
📋 TL;DR
CVE-2021-41402 is a remote code execution vulnerability in flatCore-CMS v2.0.8 that allows attackers to execute arbitrary PHP code on affected systems. This affects all organizations running vulnerable versions of flatCore-CMS, potentially leading to complete system compromise.
💻 Affected Systems
- flatCore-CMS
📦 What is this software?
Flatcore Cms by Flatcore
⚠️ Risk & Real-World Impact
Worst Case
Complete server takeover, data theft, ransomware deployment, and lateral movement to other systems.
Likely Case
Website defacement, data exfiltration, and installation of backdoors or cryptocurrency miners.
If Mitigated
Limited impact with proper network segmentation, web application firewalls, and minimal privileges.
🎯 Exploit Status
The vulnerability is well-documented in public GitHub issues with technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v2.0.9 or later
Vendor Advisory: https://github.com/flatCore/flatCore-CMS/issues/59
Restart Required: No
Instructions:
1. Backup your current installation. 2. Download the latest version from the official repository. 3. Replace all files except configuration and user data. 4. Verify functionality.
🔧 Temporary Workarounds
Web Application Firewall
allDeploy a WAF with RCE protection rules to block exploitation attempts.
File Upload Restrictions
linuxImplement strict file upload validation and disable PHP execution in upload directories.
# Add to .htaccess in upload directories:
<Files *.php>
Order Deny,Allow
Deny from all
</Files>
🧯 If You Can't Patch
- Isolate the affected system from critical networks and implement strict network segmentation.
- Implement application allowlisting and disable unnecessary PHP functions via php.ini.
🔍 How to Verify
Check if Vulnerable:
Check the CMS version in the admin panel or by examining the core files for version 2.0.8.Check Version:
Check the version.php file or admin dashboard for version information.Verify Fix Applied:
Verify the version has been updated to 2.0.9 or later and test file upload functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads to CMS directories
- Suspicious PHP execution in logs
- Unexpected system commands in web logs
Network Indicators:
- HTTP requests with malicious file uploads
- Outbound connections from web server to suspicious IPs
SIEM Query:
source="web_logs" AND (url="*upload*" AND (file_extension="php" OR file_extension="phtml"))