About File Upload Vulnerabilities
File upload vulnerabilities occur when applications allow users to upload files without proper validation, leading to various security issues including remote code execution, server compromise, and data breaches.
Common File Upload Attack Types
Basic File Upload: Simple file upload without validation
Filter Bypass: Bypassing file type and content filters
Web Shell: Uploading malicious web shells for server control
Advanced Techniques: Complex methods to bypass modern protections
RCE via Upload: Achieving Remote Code Execution through file upload
Common Vulnerable Functions
PHP: move_uploaded_file(), $_FILES, file_get_contents()
Python: request.files, werkzeug, flask uploads
Node.js: multer, formidable, express-fileupload
Java: MultipartFile, Commons FileUpload
C#: IFormFile, HttpPostedFileBase
Real-World Impact
Remote Code Execution (RCE)
Server compromise and data breaches
Web shell installation and persistence
Data exfiltration and sensitive information disclosure
Denial of Service (DoS) attacks
Compliance violations and security breaches