CVE-2020-20979
📋 TL;DR
This vulnerability allows attackers to upload arbitrary files to LJCMS v4.3 web servers through the move_uploaded_file() function, potentially leading to remote code execution. Any organization running LJCMS v4.3 is affected. Attackers can upload malicious files like PHP shells to gain control of the server.
💻 Affected Systems
- LJCMS
📦 What is this software?
Ljcms by 8cms
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise with attacker gaining root/admin access, data exfiltration, ransomware deployment, and use as pivot point for internal network attacks.
Likely Case
Webshell installation leading to website defacement, data theft, cryptocurrency mining, or use in botnets.
If Mitigated
File upload attempts blocked or quarantined with no code execution possible.
🎯 Exploit Status
Simple file upload bypass techniques can be used. No authentication required to exploit in default configurations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: None available
Restart Required: No
Instructions:
1. Check if newer LJCMS versions exist from official sources
2. If no patch available, implement workarounds immediately
3. Consider migrating to alternative CMS if LJCMS is no longer maintained
🔧 Temporary Workarounds
File Upload Restriction
allImplement strict file type validation and extension filtering for uploads
# In PHP configuration or application code
# Add file extension whitelist
$allowed_extensions = ['jpg', 'png', 'pdf'];
# Implement MIME type checking
if (!in_array($_FILES['file']['type'], $allowed_mime_types)) {
die('Invalid file type');
}
Upload Directory Protection
linuxPrevent execution of uploaded files in upload directories
# In .htaccess for Apache
<FilesMatch "\.(php|php5|phtml|pl|cgi)">
Order Deny,Allow
Deny from all
</FilesMatch>
# In nginx configuration
location ~* \.(php|php5|phtml|pl|cgi)$ {
deny all;
}
🧯 If You Can't Patch
- Disable file upload functionality completely in LJCMS
- Implement web application firewall (WAF) rules to block suspicious file uploads
🔍 How to Verify
Check if Vulnerable:
Check LJCMS version in admin panel or by examining source files. Look for version 4.3 in configuration files or database.Check Version:
# Check LJCMS version in PHP files
grep -r "version.*4.3" /path/to/ljcms/ || find /path/to/ljcms/ -name "*.php" -exec grep -l "LJCMS.*4.3" {} \;Verify Fix Applied:
Test file upload functionality with malicious file extensions (.php, .phtml) - they should be rejected. Verify upload directory has execution restrictions.📡 Detection & Monitoring
Log Indicators:
- Multiple failed file upload attempts
- Uploads of non-image files to upload directories
- HTTP POST requests to upload endpoints with PHP/executable extensions
Network Indicators:
- Unusual outbound connections from web server
- Large file uploads to unexpected paths
- POST requests with executable file content
SIEM Query:
source="web_logs" (method="POST" AND uri="*upload*" AND (extension="php" OR extension="phtml" OR extension="pl"))