CVE-2020-25406
📋 TL;DR
This vulnerability in LemoCMS 1.8.x allows authenticated users to upload executable files through the upload functionality, bypassing intended file type restrictions. Attackers can upload malicious files like PHP scripts or other executables to gain unauthorized access or execute arbitrary code on the server. This affects all installations of LemoCMS 1.8.x with the vulnerable upload controller.
💻 Affected Systems
- LemoCMS
📦 What is this software?
Lemocms by Lemocms
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise through remote code execution, allowing attackers to install backdoors, steal data, deface websites, or pivot to internal networks.
Likely Case
Website defacement, data theft, or malware distribution through uploaded malicious files that execute on the server.
If Mitigated
Limited impact with proper file upload validation, but still potential for denial of service through file upload exhaustion.
🎯 Exploit Status
Exploitation requires authenticated access to the CMS, but the file upload bypass is straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
No official patch available. Consider upgrading to a newer version if available, or implement the workarounds below.
🔧 Temporary Workarounds
Implement File Type Validation
allAdd server-side validation to restrict uploaded files to safe extensions only (e.g., .jpg, .png, .pdf) and verify file content types.
Modify app/admin/controller/sys/Uploads.php to add validation checks
Restrict Upload Directory Permissions
linuxSet upload directory permissions to prevent execution of uploaded files.
chmod 644 /path/to/upload/directory/*
chmod 755 /path/to/upload/directory/
🧯 If You Can't Patch
- Disable the upload functionality completely if not needed
- Implement a web application firewall (WAF) with file upload protection rules
🔍 How to Verify
Check if Vulnerable:
Check if you can upload a file with executable extension (e.g., .php, .exe) through the CMS upload interface while authenticated.Check Version:
Check LemoCMS version in admin panel or configuration filesVerify Fix Applied:
Attempt to upload an executable file after implementing fixes - it should be rejected or saved with execution prevented.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with executable extensions
- Multiple failed upload attempts
- Uploads from unexpected user accounts
Network Indicators:
- HTTP POST requests to upload endpoints with executable file content
- Subsequent requests to uploaded executable files
SIEM Query:
source="web_server" AND (uri="*upload*" OR uri="*Uploads*") AND (file_extension="php" OR file_extension="exe" OR file_extension="sh")