File upload attacks are a common web application vulnerability where attackers upload malicious files to execute arbitrary code, deface websites, or compromise servers. Below, we explore key techniques, prevention methods, and practical commands to secure your systems.
You Should Know:
1. Common File Upload Attack Vectors
- Malicious File Execution: Uploading
.php,.jsp, or `.aspx` files to execute server-side code. - File Overwrite: Replacing critical system files (e.g.,
.htaccess). - Zip/TAR Bomb: Uploading compressed files that expand to exhaust disk space.
2. Prevention Techniques
- Restrict File Types: Use server-side validation (not just client-side).
Example: Allow only images in Apache <FilesMatch "\.(jpg|jpeg|png|gif)$"> ForceType application/octet-stream Header set Content-Disposition attachment </FilesMatch>
- Rename Uploaded Files: Prevent directory traversal.
$new_filename = uniqid() . '.' . $ext; move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/' . $new_filename);
- Use Secure Storage: Store files outside the web root.
location /uploads/ { alias /var/secure_uploads/; deny all; }
3. Linux Commands for File Analysis
- Check file type (bypass fake extensions):
file uploads/malicious.doc
- Scan for embedded PHP in images:
strings image.jpg | grep "<?php"
- Detect zip bombs:
ls -lh suspicious.zip Check size before extraction
4. Windows Defender for File Upload Protection
- Block dangerous extensions via PowerShell:
Add-MpPreference -ExtensionExclusion ".exe,.php,.js"
- Scan uploads automatically:
Start-MpScan -ScanPath "C:\uploads" -ScanType FullScan
What Undercode Say:
File upload vulnerabilities remain a top attack vector due to misconfigurations and weak validation. Always:
– Use server-side checks (MIME type, magic bytes).
– Isolate uploads in sandboxed environments.
– Monitor logs for suspicious activity:
tail -f /var/log/apache2/access.log | grep "POST /upload"
– Employ Web Application Firewalls (WAFs) like ModSecurity:
SecRule FILES "@rx .php$" "deny,log,msg:'Blocked PHP upload'"
Expected Output:
A secure file upload system that:
- Rejects executable files.
- Logs all upload attempts.
- Stores files safely outside web directories.
Prediction:
As cloud storage grows, attackers will increasingly exploit file upload APIs and serverless functions. Zero-trust file validation will become critical.
Relevant Course Links:
References:
Reported By: Zlatanh File – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
