CVE-2020-21489
📋 TL;DR
CVE-2020-21489 is a critical file upload vulnerability in Feehicms v2.0.8 that allows remote attackers to upload malicious files and execute arbitrary code on the server. This affects all Feehicms v2.0.8 installations with the vulnerable admin-user/update-self component accessible.
💻 Affected Systems
- Feehicms
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise leading to data theft, ransomware deployment, or use as a foothold for lateral movement within the network.
Likely Case
Webshell installation allowing persistent backdoor access, data exfiltration, and further exploitation of the server.
If Mitigated
Attack blocked at the web application firewall level or by file upload restrictions, preventing code execution.
🎯 Exploit Status
Exploitation requires authentication to the admin interface. The vulnerability is well-documented in public repositories with proof-of-concept examples available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v2.0.9 or later
Vendor Advisory: https://github.com/liufee/cms/issues/46
Restart Required: No
Instructions:
1. Backup your current Feehicms installation and database. 2. Download the latest version from the official repository. 3. Replace the vulnerable files with the patched version. 4. Verify the update by checking the version number.
🔧 Temporary Workarounds
Restrict Admin Access
allLimit access to the admin interface to trusted IP addresses only
# Add to .htaccess or web server config
Order Deny,Allow
Deny from all
Allow from 192.168.1.0/24
File Upload Restrictions
allImplement strict file upload validation and whitelisting
# Example PHP validation
$allowed_types = ['image/jpeg', 'image/png'];
$allowed_ext = ['jpg', 'jpeg', 'png'];
# Validate both MIME type and file extension
🧯 If You Can't Patch
- Disable the vulnerable /admin/index.php?r=admin-user%2Fupdate-self endpoint completely
- Implement a Web Application Firewall (WAF) with rules to block malicious file uploads and PHP execution attempts
🔍 How to Verify
Check if Vulnerable:
Check if running Feehicms v2.0.8 and if the /admin/index.php?r=admin-user%2Fupdate-self endpoint is accessibleCheck Version:
Check the version.php file or admin dashboard for version informationVerify Fix Applied:
Verify the version is updated to v2.0.9 or later and test file upload functionality with malicious payloads📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads to admin-user/update-self endpoint
- PHP file uploads with suspicious names
- Multiple failed upload attempts followed by successful upload
Network Indicators:
- POST requests to /admin/index.php?r=admin-user%2Fupdate-self with file uploads
- Subsequent requests to uploaded PHP files
SIEM Query:
source="web_logs" AND uri="/admin/index.php" AND query="r=admin-user%2Fupdate-self" AND method="POST" AND size>100000