CVE-2021-43741
📋 TL;DR
CMSimple 5.4 contains a directory traversal vulnerability in config.php that allows attackers to manipulate file names to execute arbitrary code remotely. This affects all systems running CMSimple 5.4, potentially compromising the entire web server.
💻 Affected Systems
- CMSimple
📦 What is this software?
Cmsimple by Cmsimple
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise with attacker gaining complete control over the web server, data theft, malware deployment, and lateral movement to other systems.
Likely Case
Website defacement, data exfiltration, and installation of backdoors or cryptocurrency miners on the affected server.
If Mitigated
Limited impact with only web application compromise if proper network segmentation and least privilege are implemented.
🎯 Exploit Status
Public proof-of-concept code exists on GitHub. Exploitation requires minimal technical skill.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.5 or later
Vendor Advisory: https://github.com/iiSiLvEr/CMSimple5.4-Vulnerabilities
Restart Required: No
Instructions:
1. Backup your CMSimple installation and database. 2. Download CMSimple 5.5 or later from the official repository. 3. Replace all files except user-generated content. 4. Verify the installation works correctly.
🔧 Temporary Workarounds
Restrict file upload permissions
linuxModify file permissions to prevent unauthorized file writes to config.php directory
chmod 644 config.php
chown root:www-data config.php
Web Application Firewall rule
allBlock directory traversal patterns in HTTP requests
🧯 If You Can't Patch
- Isolate the CMSimple server in a DMZ with strict outbound firewall rules
- Implement file integrity monitoring on config.php and surrounding directories
🔍 How to Verify
Check if Vulnerable:
Check if CMSimple version is 5.4 by examining the admin panel or checking version files in the installation directory.Check Version:
grep -r 'version.*5\.4' /path/to/cmsimple/ || cat /path/to/cmsimple/cmsimple/version.txtVerify Fix Applied:
Verify the version has been updated to 5.5 or later and test directory traversal attempts return proper error messages.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns to config.php
- HTTP requests containing '../' or similar traversal patterns
- Unexpected file writes in CMSimple directories
Network Indicators:
- HTTP POST requests to config.php with unusual parameters
- Outbound connections from web server to unknown IPs
SIEM Query:
source="web_logs" AND (uri="*config.php*" AND (param="*../*" OR param="*..\\*"))