A comprehensive guide to securing file uploads in PHP, covering five common vulnerabilities in naive upload code and how to fix them. Topics include server-side MIME detection using finfo magic bytes, safe extension allowlisting to block double-extension attacks, polyglot file defense via GD/Imagick re-encoding, enforcing size limits in PHP code rather than relying on HTML or php.ini alone, generating cryptographically random storage filenames, storing files outside the web root, serving files through an authorized PHP controller with proper security headers, and stripping EXIF metadata and validating image dimensions to prevent decompression bombs.