CVE-2021-47753
📋 TL;DR
CVE-2021-47753 is an unauthenticated file upload vulnerability in phpKF CMS that allows remote attackers to upload malicious PHP files disguised as PNG images, bypass file extension checks, rename them, and execute arbitrary system commands via web shell parameters. This affects all systems running phpKF CMS 3.00 Beta y6 without proper file upload validation.
💻 Affected Systems
- phpKF CMS
📦 What is this software?
Cms by Phpkf
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with remote code execution, data theft, lateral movement, and persistent backdoor installation.
Likely Case
Web server compromise leading to website defacement, data exfiltration, and cryptocurrency mining malware deployment.
If Mitigated
Attack blocked at web application firewall level with no successful file uploads.
🎯 Exploit Status
Exploit code is publicly available on Exploit-DB and requires minimal technical skill to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: https://www.phpkf.com/
Restart Required: No
Instructions:
No official patch exists. Upgrade to a newer version if available or implement workarounds.
🔧 Temporary Workarounds
Restrict File Upload Extensions
allConfigure web server to block PHP file uploads and only allow specific safe extensions.
# In Apache .htaccess:
<FilesMatch "\.(php|phtml|php3|php4|php5|php7|phps|inc)$">
Order Allow,Deny
Deny from all
</FilesMatch>
# In Nginx config:
location ~ \.(php|phtml|php3|php4|php5|php7|phps|inc)$ {
deny all;
}
Disable File Upload Functionality
allTemporarily disable file upload features in phpKF CMS configuration.
# Edit phpKF configuration to remove upload capabilities
🧯 If You Can't Patch
- Immediately isolate affected systems from internet access
- Implement strict network segmentation and monitor for suspicious file upload activity
🔍 How to Verify
Check if Vulnerable:
Check phpKF CMS version in admin panel or configuration files. If version is 3.00 Beta y6, system is vulnerable.Check Version:
Check phpKF configuration files or admin interface for version information.Verify Fix Applied:
Test file upload functionality with PHP files disguised as PNGs. If upload is blocked or fails, fix may be working.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with .png extensions followed by .php file access
- Multiple failed upload attempts with different file names
- Web shell parameter patterns in URL access logs
Network Indicators:
- HTTP POST requests to upload endpoints with unusual file content
- Subsequent requests to uploaded files with system command parameters
SIEM Query:
source="web_logs" AND (uri="*upload*" AND file_extension="png") AND (uri="*.php" AND params="*cmd=*" OR params="*system=*")