Need

Enforcement of data uniqueness verification

Context

• Usage of C# 7.1 for developing applications with advanced language features
• Usage of Microsoft.AspNetCore.Mvc for building web applications with ASP.NET Core
• Usage of Microsoft.AspNetCore.Identity for managing user authentication and authorization in ASP.NET Core applications
• Usage of Microsoft.AspNetCore.Identity.EntityFrameworkCore for managing user authentication and authorization in ASP.NET Core applications

Description

Non compliant code

        public class UserController : Controller
{
    private readonly UserManager _userManager;

    public UserController(UserManager userManager)
    {
        _userManager = userManager;
    }

    [HttpPost]
    public async Task Register(RegisterViewModel model)
    {
        if (ModelState.IsValid)
        {
            var user = new IdentityUser { UserName = model.Email, Email = model.Email };
            var result = await _userManager.CreateAsync(user, model.Password);

            if (result.Succeeded)
            {
                return RedirectToAction("Index", "Home");
            }
        }

        return View(model);
    }
}
        
        

In the above code, we have a UserController with a Register action. The Register action creates a new user based on the provided email and password.

The vulnerability lies in the fact that the code does not check for the uniqueness of the email before creating a new user. This means that multiple users can register with the same email address, which should not be allowed.

This can lead to various issues, including:

1. Account Takeover: If an attacker can guess or know the password of a user, they can register a new account with the same email and gain access to the user's account.

2. Data Inconsistency: Multiple users with the same email can lead to data inconsistency and confusion.

3. Account Recovery Issues: If a user forgets their password and tries to recover their account, the recovery email might be sent to the wrong user.

In a nutshell, not properly validating the uniqueness of the data (in this case, the email) can lead to serious security issues and data inconsistency.

Steps

• Implement server-side validation to ensure data uniqueness.
• Before creating a new user, check if the email address is already registered.
• If the email address is already registered, display an error message to the user.
• Consider using a unique constraint in the database to enforce data uniqueness.
• Ensure that the validation is performed at the application layer and not solely relying on client-side validation.

Compliant code

        public class UserController : Controller
{
    private readonly UserManager _userManager;

    public UserController(UserManager userManager)
    {
        _userManager = userManager;
    }

    [HttpPost]
    public async Task Register(RegisterViewModel model)
    {
        if (ModelState.IsValid)
        {
            var existingUser = await _userManager.FindByEmailAsync(model.Email);
            if(existingUser != null)
            {
                ModelState.AddModelError("", "Email already registered");
                return View(model);
            }

            var user = new IdentityUser { UserName = model.Email, Email = model.Email };
            var result = await _userManager.CreateAsync(user, model.Password);

            if (result.Succeeded)
            {
                return RedirectToAction("Index", "Home");
            }
        }

        return View(model);
    }
}
        
        

The updated code now includes a server-side validation to ensure the uniqueness of the user's email. Before creating a new user, the application checks if the email address is already registered. This is done by calling the FindByEmailAsync method of the UserManager class, which returns a user if one exists with the specified email, or null if no such user exists.

If a user with the specified email already exists ( existingUser != null), an error message is added to the ModelState and the registration view is returned, displaying the error message to the user.

If no user with the specified email exists, the application proceeds to create a new user as before.

This server-side validation ensures that each email address can only be registered once, preventing an attacker from reusing or regenerating information that should be valid for one use only. It is important to note that this validation should be performed at the application layer and not solely rely on client-side validation, as client-side validation can be bypassed by an attacker.

References

• 095. Data uniqueness not properly verified