CVE-2023-23328
📋 TL;DR
This vulnerability allows authenticated users to upload malicious PHP files to AvantFAX servers by bypassing file type validation. Attackers can execute arbitrary code on the server, potentially compromising the entire system. Only AvantFAX 3.3.7 installations with authenticated user access are affected.
💻 Affected Systems
- AvantFAX
📦 What is this software?
Avantfax by Avantfax
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise leading to data theft, ransomware deployment, or use as a pivot point into internal networks.
Likely Case
Webshell installation allowing persistent access, data exfiltration, and further lateral movement within the network.
If Mitigated
Limited to authenticated user's privileges if proper file upload restrictions and web application firewalls are in place.
🎯 Exploit Status
Exploit requires authenticated access but is trivial to execute once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch available. Consider upgrading to a newer version if available or implementing workarounds.
🔧 Temporary Workarounds
Restrict PHP file uploads via web server
linuxConfigure web server to block PHP file execution in upload directories
For Apache: Add 'php_flag engine off' to .htaccess in upload directory
For Nginx: Add 'location ~ \.php$ { deny all; }' to upload directory config
Implement file extension whitelisting
allModify FileUpload.php to only allow specific safe file extensions
Edit FileUpload.php to replace current validation with: $allowed = ['pdf', 'jpg', 'png', 'txt']; if(!in_array($ext, $allowed)) { die('Invalid file type'); }
🧯 If You Can't Patch
- Disable file upload functionality completely in AvantFAX configuration
- Implement strict network segmentation to isolate AvantFAX server from critical systems
🔍 How to Verify
Check if Vulnerable:
Attempt to upload a PHP file with .php extension while authenticated; if successful, system is vulnerable.Check Version:
Check AvantFAX version in web interface or configuration filesVerify Fix Applied:
Attempt same upload test; file should be rejected or saved without execution capability.📡 Detection & Monitoring
Log Indicators:
- PHP file uploads in web server logs
- Unusual POST requests to FileUpload.php
- Webshell access patterns in logs
Network Indicators:
- Unexpected outbound connections from AvantFAX server
- POST requests with PHP file content
SIEM Query:
source="web.log" AND (uri="/FileUpload.php" OR file_extension=".php") AND user_agent NOT IN ["normal_user_agents"]