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Lack of data validation - Dates

Need​

Implementation of robust data validation for date fields

Context​

  • Usage of C# for building robust and scalable applications
  • Usage of _context for managing state and data in the application
  • Usage of UserUpdateModel for updating user information
  • Usage of IActionResult for handling and returning HTTP responses in an application
  • Usage of NotFound for handling 404 errors in a web application
  • Usage of NoContent for handling HTTP responses with no content

Description​

Non compliant code​

[HttpPost]
public async Task<IActionResult> UpdateUser(int id, UserUpdateModel model)
{
    var user = await _context.Users.FindAsync(id);

    if (user == null)
    {
        return NotFound();
    }

    user.DateOfBirth = model.DateOfBirth;
    user.Email = model.Email;

    await _context.SaveChangesAsync();

    return NoContent();
}

The above code is a typical example of a method in an ASP.NET Core controller that updates a user's information. The UpdateUser method is vulnerable because it lacks server-side validation for the incoming data.

The UserUpdateModel object, model, contains the data that the client (frontend) sends in the HTTP request. The method directly assigns the DateOfBirth and Email fields from the model to the user object without validating these fields.

This lack of validation means that a malicious user can potentially send invalid or malicious data in these fields. For example, the user can send a future date in the DateOfBirth field, or an email that doesn't match the standard format.

The server will accept this data and save it to the database, leading to data corruption, inconsistencies, or potential security issues.

In the case of the DateOfBirth field, it's especially critical to validate that the date is not in the future, and that it is a valid date. In the case of the Email field, the application should validate that the email is in a valid format.

This vulnerability could be exploited by an attacker to bypass the frontend restrictions and send requests that the server does not validate, but processes as valid requests.

Steps​

  • Implement server-side validation for the date of birth field to ensure it is a valid date.
  • Implement server-side validation for the email field to ensure it is a valid email address.
  • Check the user's permissions before allowing the update operation.
  • Consider using a role-based access control system to manage user permissions.
  • Implement proper error handling and return appropriate error responses when validation fails or permissions are not granted.

Compliant code​

[HttpPost]
public async Task<IActionResult> UpdateUser(int id, UserUpdateModel model)
{
    var user = await _context.Users.FindAsync(id);

    if (user == null)
    {
        return NotFound();
    }

    // Validate Date of Birth
    if (!DateTime.TryParse(model.DateOfBirth, out DateTime dob))
    {
        return BadRequest("Invalid Date of Birth");
    }

    // Validate Email
    if (!Regex.IsMatch(model.Email, @"^[\\w-]+(\\.[\\w-]+)*@([\\w-]+\\.)+[a-zA-Z]{2,7}$"))
    {
        return BadRequest("Invalid Email Address");
    }

    // Check user permissions
    // This is a placeholder, replace with your actual permission checking logic
    if (!UserHasPermission(user))
    {
        return Unauthorized();
    }

    user.DateOfBirth = dob;
    user.Email = model.Email;

    await _context.SaveChangesAsync();

    return NoContent();
}

private bool UserHasPermission(User user)
{
    // Implement your permission checking logic here
    // Return true if the user has permission, false otherwise
    return true;
}

The updated code now includes server-side validation for both the date of birth and email fields.

For the date of birth, we use DateTime.TryParse to check if the provided date of birth is a valid date. If it's not, we return a BadRequest with a message indicating that the date of birth is invalid.

For the email, we use a regular expression to check if the provided email is in a valid format. If it's not, we return a BadRequest with a message indicating that the email address is invalid.

We also check if the user has permission to update the user details. This is done in the UserHasPermission method, which should be replaced with your actual permission checking logic. If the user does not have permission, we return an Unauthorized response.

These changes ensure that the server does not process invalid requests and that only authorized users can update user details.

References​

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