What common mistake do developers make with Uploaded files, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Uploaded files, why does the mistake cause problems, and what is the safer approach? One recurring problem with uploaded files is applying it without understanding the boundary it protects. Trusting raw input and using it directly in database updates or application decisions without validation and authorization. In addition, Uploaded files can be accessed through request file methods and validated before storage. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.