Input Validation for MVC CASENET Practice Questions (Page 5)

Questions 21–25

1. 21foundation · easy

   Why is it important to validate the size of an uploaded file?

   • ATo check if the file is a valid image
   • BTo prevent denial-of-service attacks that exhaust server storage or memory
   • CTo verify the file's MIME type
   • DTo ensure the file is not corrupted
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2. 22expert · hard

   An MVC application allows users to upload documents. The security team requires that only PDF files are accepted. The developer implements validation that checks the file extension is '.pdf' and the MIME type is 'application/pdf'. A penetration test reveals that an attacker can upload a file with a '.pdf' extension and MIME type 'application/pdf' that is actually an executable. Which additional validation is most effective?

   • AUse a blacklist of dangerous file signatures to reject known executable formats.
   • BCheck the file size and reject files larger than a certain threshold.
   • CStore the file with a random name and no extension on the server.
   • DInspect the file's magic bytes to verify the content starts with '%PDF'.
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4. 23application · medium

   A healthcare portal has a registration form where users must provide a date of birth. The business rule states that users must be at least 18 years old to register. The development team wants to enforce this rule using declarative validation on the model so that it is automatically checked during model binding and the error is displayed in the validation summary. Which approach should the team use?

   • AImplement validation logic in the view using JavaScript to compare the entered date with the current date and block form submission if the user is under 18.
   • BAdd a [RegularExpression] attribute with a pattern that matches dates more than 18 years in the past.
   • CCreate a custom validation attribute that inherits from ValidationAttribute and override the IsValid method to compare the date against DateTime.Today.AddYears(-18).
   • DApply a [Range] attribute with the minimum date set to DateTime.Today.AddYears(-18) and the maximum date set to DateTime.Today.
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5. 24application · medium

   A user registration form in an MVC application includes a Username field. The business requirement is to provide immediate feedback to the user if the username is already taken, without submitting the entire form. The application uses jQuery unobtrusive validation. Which approach should the developer use?

   • AWrite a custom jQuery AJAX call in the view that checks the username and displays an error message manually.
   • BAdd [Remote(action: "CheckUsername", controller: "Account")] to the Username property and implement a controller action that returns JsonResult with true or false.
   • CAdd [RegularExpression(@"^[a-zA-Z0-9]+")] to the Username property and rely on client-side pattern matching.
   • DAdd [Required] to the Username property and perform the uniqueness check only when the form is submitted.
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6. 25foundation · easy

   What is the purpose of the Remote validation attribute in ASP.NET MVC?

   • ATo encrypt data before sending it to the server
   • BTo validate data on the client without contacting the server
   • CTo validate data on a remote database server
   • DTo perform asynchronous server-side validation from the client without a full page postback
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