S6932 — Use model binding instead of reading raw request data

The HttpRequest class provides access to the raw request data through the QueryString, Headers, and Forms properties. However, whenever possible it is recommended to use model binding instead of directly accessing the input data.

Why is this an issue?

Both ASP.Net MVC implementations - Core and Framework - support model binding in a comparable fashion. Model binding streamlines the process by automatically aligning data from HTTP requests with action method parameters, providing numerous benefits compared to manually parsing raw incoming request data:

Simplicity

Model binding simplifies the code by automatically mapping data from HTTP requests to action method parameters. You don’t need to write any code to manually extract values from the request.

Type Safety

Model binding provides type safety by automatically converting the incoming data into the appropriate .NET types. If the conversion fails, the model state becomes invalid, which you can easily check using ModelState.IsValid.

Validation

With model binding, you can easily apply validation rules to your models using data annotations. If the incoming data doesn’t comply with these rules, the model state becomes invalid.

Security

Model binding helps protect against over-posting attacks by only including properties in the model that you explicitly bind using the [Bind] attribute or by using view models that only contain the properties you want to update.

Maintainability

By using model binding, your code becomes cleaner, easier to read, and maintain. It promotes the use of strongly typed views, which can provide compile-time checking of your views.

How to fix it in ASP.NET Core

Request.Form, Request.Form.Files, Request.Headers, Request.Query and Request.RouteValues are keyed collections that expose data from the incoming HTTP request:

• Request.Form - application/x-www-form-urlencoded form data from the HTTP request body
• Request.Form.Files - multipart/form-data file data from the HTTP request body
• Request.Headers - HTTP Header values
• Request.Query - URL parameter values
• Request.RouteValues - Values extracted from the path portion of the URL

Model binding can bind these keyed collections to

• action method parameters by matching the key to the parameter name or
• the property of a complex type by matching the key to the property name.

To replace the keyed collection access, you can:

The Model Binding in ASP.NET Core article describes the mechanisms, conventions, and customization options for model binding in more detail. Route-based binding is described in the Routing to controller actions in ASP.NET Core document.

Code examples

Noncompliant code example

public IActionResult Post()
{
    var name = Request.Form["name"];                           // Noncompliant: Request.Form
    var birthdate = DateTime.Parse(Request.Form["Birthdate"]); // Noncompliant: Request.Form

    var locale = Request.Query.TryGetValue("locale", out var locales)
        ? locales.ToString()
        : "en-US";                                             // Noncompliant: Request.Query
    // ..
}

Compliant solution

public record User
{
    [Required, StringLength(100)]
    public required string Name { get; init; }
    [DataType(DataType.Date)]
    public DateTime? Birthdate { get; init; }
}

public IActionResult Post(User user, [FromHeader] string origin, [FromQuery] string locale = "en-US")
{
    if (ModelState.IsValid)
    {
        // ...
    }
}

How does this work?

Model binding in ASP.NET Core MVC and ASP.NET MVC 4.x works by automatically mapping data from HTTP requests to action method parameters. Here’s a step-by-step breakdown of how it works:

1. Request Data When a user submits a form or sends a request to an ASP.NET application, the request data might include form data, query string parameters, request body, and HTTP headers.
2. Model Binder The model binder’s job is to create .NET objects from the request data. It looks at each parameter in the action method and attempts to populate it with the incoming data.
3. Value Providers The model binder uses Value Providers to get data from various parts of the request, such as the query string, form data, or route data. Each value provider tells the model binder where to find values in the request.
4. Binding The model binder tries to match the keys from the incoming data with the properties of the action method’s parameters. If a match is found, it attempts to convert the incoming data into the appropriate .NET type and assigns it to the parameter.
5. Validation If the model binder can’t convert the value or if the converted value doesn’t pass any specified validation rules, it adds an error to the ModelState.Errors collection. You can check ModelState.IsValid in your action method to see if any errors occurred during model binding.
6. Action Method Execution The action method is executed with the bound parameters. If ModelState.IsValid is false, you can handle the errors in your action method and return an appropriate response.

See the links in the Resources section for more information.

How to fix it in ASP.NET MVC 4.x

Request.Form and Request.QueryString are keyed collections that expose data from the incoming HTTP request:

• Request.Form - application/x-www-form-urlencoded form data from the HTTP request body
• Request.QueryString - URL parameter values

Model binding can bind these keyed collections to

• action method parameters by matching the key to the parameter name or
• the property of a complex type by matching the key to the property name.

To replace the keyed collection access, you can:

Code examples

Noncompliant code example

public ActionResult Post()
{
    var name = Request.Form["name"];                            // Noncompliant: Request.Form
    Debug.WriteLine(Request.Form[0]);                           // Compliant: Binding by index is not supported.
    var birthdate = DateTime.Parse(Request.Form["Birthdate"]);  // Noncompliant: Request.Form

    var cultureName = Request.QueryString["locale"] ?? "en-US"; // Noncompliant: Request.QueryString
    // ..
}

Compliant solution

public class User
{
    [Required, StringLength(100)]
    public string Name { get; set; }
    [DataType(DataType.Date)]
    public DateTime? Birthdate { get; set; }
}

public ActionResult Post(User user, [Bind(Prefix = "locale")] string cultureName = "en-US")
{
    if (ModelState.IsValid)
    {
        // ...
    }
}

public IActionResult Post()
{
    var origin = Request.Headers[HeaderNames.Origin];          // Compliant: Access via non-constant field
    var nameField = "name";
    var name = Request.Form[nameField];                        // Compliant: Access via local
    var birthdate = DateTime.Parse(Request.Form["Birthdate"]); // Compliant: Access via constant and variable keys is mixed.
                                                               // Model binding would only work partially in the method, so we do not raise here.
    return Ok();
    // ..
}

How does this work?

Model binding in ASP.NET Core MVC and ASP.NET MVC 4.x works by automatically mapping data from HTTP requests to action method parameters. Here’s a step-by-step breakdown of how it works:

1. Request Data When a user submits a form or sends a request to an ASP.NET application, the request data might include form data, query string parameters, request body, and HTTP headers.
2. Model Binder The model binder’s job is to create .NET objects from the request data. It looks at each parameter in the action method and attempts to populate it with the incoming data.
3. Value Providers The model binder uses Value Providers to get data from various parts of the request, such as the query string, form data, or route data. Each value provider tells the model binder where to find values in the request.
4. Binding The model binder tries to match the keys from the incoming data with the properties of the action method’s parameters. If a match is found, it attempts to convert the incoming data into the appropriate .NET type and assigns it to the parameter.
5. Validation If the model binder can’t convert the value or if the converted value doesn’t pass any specified validation rules, it adds an error to the ModelState.Errors collection. You can check ModelState.IsValid in your action method to see if any errors occurred during model binding.
6. Action Method Execution The action method is executed with the bound parameters. If ModelState.IsValid is false, you can handle the errors in your action method and return an appropriate response.

See the links in the Resources section for more information.

Resources

Documentation

• Microsoft Learn - Asp.Net Core - Model Binding in ASP.NET Core
• Microsoft Learn - Asp.Net Core - Model validation in ASP.NET Core MVC and Razor Pages
• Microsoft Learn - Asp.Net Core - Custom Model Binding in ASP.NET Core
• Microsoft Learn - Asp.Net Core - HttpRequest.Form Property
• Microsoft Learn - Asp.Net Core - IFormCollection.Files Property
• Microsoft Learn - Asp.Net Core - HttpRequest.Headers Property
• Microsoft Learn - Asp.Net Core - HttpRequest.Query Property
• Microsoft Learn - Asp.Net Core - HttpRequest.RouteValues Property
• Microsoft Learn - Asp.Net Core - FormCollection Class
• Microsoft Learn - Asp.Net Core - IFormFile Interface
• Microsoft Learn - Asp.Net Core - IFormFileCollection Interface
• Microsoft Learn - Asp.Net Core - BindAttribute Class
• Microsoft Learn - ASP.NET MVC 4.x - Parameter Binding in ASP.NET Web API
• Microsoft Learn - ASP.NET MVC 4.x - Adding a New Controller
• Microsoft Learn - ASP.NET MVC 4.x - Adding a New Model
• Microsoft Learn - ASP.NET MVC 4.x - Adding Validation
• Microsoft Learn - ASP.NET MVC 4.x - Model Validation in ASP.NET Web API
• Microsoft Learn - ASP.NET MVC 4.x - HttpRequest.Form Property
• Microsoft Learn - ASP.NET MVC 4.x - HttpRequest.QueryString Property
• Microsoft Learn - ASP.NET MVC 4.x - BindAttribute Class
• MDN - HTTP request methods > POST
• MDN - Request header
• MDN - What is a URL?