Need

Secure and granular access control mechanisms

Context

• Usage of C# for building robust and scalable applications
• Usage of _context for managing state and data in a specific context
• Usage of NotFound for handling 404 errors in a web application
• Usage of Ok for handling HTTP responses with status code 200

Description

Non compliant code

        [HttpGet]
public IActionResult GetUser(string id)
{
    var user = _context.Users.SingleOrDefault(u => u.Id == id);
    if (user == null)
    {
        return NotFound();
    }

    return Ok(user);
}
        
        

The above code is an example of an insecure direct object reference (IDOR) vulnerability. The GetUser method takes an id as a parameter and uses it to look up a user in the database. If a user is found, their details are returned in the response.

The vulnerability here is that there is no check to ensure that the user requesting the data is authorized to view it. As a result, an attacker could potentially manipulate the id parameter to gain access to other users' data.

For instance, if an attacker knows or guesses the id of another user, they can simply replace their own id with the other user's id in the request. The system will then return the other user's data, as it does not check whether the requester has the right to access this data.

This is a serious security issue as it can lead to unauthorized access to sensitive user data.

Steps

• Implement proper authentication and authorization mechanisms to ensure that only authenticated and authorized users can access the GetUser endpoint.
• Use session management or token-based authentication to securely identify and authenticate users.
• Ensure that the user making the request has the necessary permissions to access the requested user's data.
• Avoid using user-provided input directly in database queries. Instead, use parameterized queries or an ORM framework to prevent SQL injection attacks.
• Implement proper input validation to ensure that the 'id' parameter is valid and belongs to the authenticated user.
• Consider implementing role-based access control (RBAC) to restrict access to sensitive user data based on user roles and permissions.
• Regularly update and patch the application and its dependencies to address any security vulnerabilities that may arise.

Compliant code

        [HttpGet]
[Authorize]
public IActionResult GetUser(string id)
{
    var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
    if (userId != id)
    {
        return Unauthorized();
    }

    var user = _context.Users.SingleOrDefault(u => u.Id == id);
    if (user == null)
    {
        return NotFound();
    }

    return Ok(user);
}
        
        

The updated code now includes an [Authorize] attribute on the GetUser method. This attribute ensures that only authenticated users can access this endpoint. If a user is not authenticated, the server will respond with a 401 Unauthorized status code.

Inside the GetUser method, we retrieve the authenticated user's ID from the User object's claims. The User object is automatically populated by ASP.NET Core when a user is authenticated.

We then compare the authenticated user's ID with the id parameter. If they do not match, we return a 403 Unauthorized status code. This ensures that users can only access their own data, not other users' data.

Finally, we query the database for the user with the provided id. If no such user exists, we return a 404 Not Found status code. If the user does exist, we return the user's data.

This code fixes the insecure direct object reference vulnerability by ensuring that only authenticated users can access the GetUser endpoint and that users can only access their own data. It also continues to handle the case where a user does not exist.

References

• 013. Insecure object reference