Lack of data validation - Numbers - Csharp

Need

Implementation of robust data validation for numbers

Context

1. Usage of C# 7.0 for modern language features and enhancements
2. Usage of Microsoft.AspNetCore.Mvc for building web applications with ASP.NET Core
3. Usage of Microsoft.EntityFrameworkCore for data access and object-relational mapping (ORM) in .NET applications

Description

Insecure Code Example

public class ProductController : Controller
{
    [HttpPost]
    public IActionResult Create(string name, int price)
    {
        var product = new Product(name, price);
        _context.Products.Add(product);
        _context.SaveChanges();

        return Ok();
    }
}

In the above code, the `Create` method of the `ProductController` class is vulnerable due to the lack of data validation. The method accepts a `name` and a `price` as parameters and directly uses these to create a new `Product` object, which is then added to the `Products` collection in the `_context` object and saved to the database. The vulnerability lies in the fact that there is no validation performed on the `price` parameter. If a negative number, zero, or an unreasonably large number is passed as the price, the method will still proceed to create the `Product` object and save it to the database. This could lead to incorrect data being stored, which could break the business logic and negatively impact the business. For example, if a negative price is saved, this could lead to incorrect calculations when determining the total cost of a set of products. Similarly, if an unreasonably large price is saved, this could lead to incorrect calculations that exceed the maximum value that can be stored in an integer, causing an overflow error. Furthermore, the lack of validation could also open up the possibility for SQL Injection attacks if the `price` parameter is used in a SQL query. Thus, it's crucial to add proper data validation to ensure that only valid prices are allowed to be saved to the database.

Steps

1. Implement input validation for the 'name' parameter to ensure it is not empty or null.
2. Implement input validation for the 'price' parameter to ensure it is a valid positive number.
3. Handle validation errors and return appropriate error responses to the client.
4. Consider using data annotations or a validation library to simplify the validation process.
5. Ensure that the validation is performed both on the client-side and server-side to provide a robust defense against malicious input.

Secure Code Example

using System.ComponentModel.DataAnnotations;

public class ProductModel
{
    [Required]
    public string Name { get; set; }

    [Required]
    [Range(1, int.MaxValue, ErrorMessage = "Please enter a value bigger than {1}")]
    public int Price { get; set; }
}

public class ProductController : Controller
{
    [HttpPost]
    public IActionResult Create([FromBody] ProductModel productModel)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        var product = new Product(productModel.Name, productModel.Price);
        _context.Products.Add(product);
        _context.SaveChanges();

        return Ok();
    }
}

The code above fixes the vulnerability by adding data validation to the `Create` method in the `ProductController` class. Firstly, a new `ProductModel` class is created to represent the incoming product data. This class includes two properties: `Name` and `Price`. Both properties are decorated with the `[Required]` attribute to ensure that they are not null or empty. The `Price` property is also decorated with the `[Range]` attribute to ensure that it is a positive number. In the `Create` method, the `[FromBody]` attribute is added to the `productModel` parameter to bind the incoming JSON data to the `ProductModel` object. Then, the `ModelState.IsValid` property is checked to see if the incoming data is valid according to the data annotations in the `ProductModel` class. If the data is not valid, the method returns a `BadRequest` response with the validation errors. If the data is valid, a new `Product` object is created and added to the database. The method then returns an `Ok` response to indicate that the product was successfully created. This approach ensures that only valid data is processed by the application, thereby preventing the business logic from being broken by invalid or malicious input.

References

Last updated

2023/09/18