Need

Secure access control and proper authorization mechanisms

Context

• Usage of C# for building robust and scalable applications
• Usage of _context for managing state and data sharing
• Usage of the User dependency for managing user data and authentication
• Usage of IActionResult for handling and returning HTTP responses in a structured manner

Description

Non compliant code

        [HttpPost]
public async Task EditUser(int id, [FromBody]User user)
{
    var currentUser = await _context.Users.FindAsync(id);
    if(currentUser == null)
    {
        return NotFound();
    }
    currentUser.Name = user.Name;
    currentUser.Email = user.Email;
    currentUser.Password = user.Password;
    await _context.SaveChangesAsync();

    return Ok(currentUser);
}
        
        

The above code represents an insecure object reference vulnerability. The EditUser function in the code is used to edit a user's details. The function is designed to take in an id and a User object as parameters. The id is used to find the current user in the database, and the User object is used to update the user's details.

The vulnerability lies in the fact that the id parameter is not being validated. This means that an attacker can easily change the id parameter to any value, and if a user with that id exists in the database, the attacker can modify that user's details. This is a direct object reference vulnerability because the system is directly using the user-supplied id to reference a user object in the database.

This vulnerability could lead to serious security breaches. An attacker could use this vulnerability to change other users' details, including their email and password. This could allow the attacker to take over other users' accounts, or to change their details to something inappropriate or offensive.

To fix this vulnerability, the application should validate the id parameter to ensure that the current user is authorized to modify the user with that id. This could be done by checking if the id matches the id of the current user, or by checking if the current user has the necessary permissions to modify other users.

Steps

• Implement proper authentication and authorization mechanisms to ensure that only authenticated and authorized users can access and modify user information.
• Use a secure and unique identifier for each user instead of relying on the client-provided identifier.
• Validate the user's access rights before allowing any modifications to user information.
• Implement input validation and sanitization to prevent any malicious input from being processed.
• Encrypt sensitive user information, such as passwords, before storing them in the database.
• Regularly update and patch the application and its dependencies to address any security vulnerabilities.

Compliant code

        [HttpPost]
[Authorize]
public async Task EditUser([FromBody]User user)
{
    var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
    var currentUser = await _context.Users.FindAsync(userId);
    if(currentUser == null)
    {
        return NotFound();
    }
    if(currentUser.Id != user.Id)
    {
        return Unauthorized();
    }
    currentUser.Name = user.Name;
    currentUser.Email = user.Email;
    currentUser.Password = HashPassword(user.Password);
    await _context.SaveChangesAsync();

    return Ok(currentUser);
}

private string HashPassword(string password)
{
    using (var sha256 = SHA256.Create())
    {
        var hashedBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(password));
        return BitConverter.ToString(hashedBytes).Replace("-", "").ToLower();
    }
}
        
        

The updated code now includes the [Authorize] attribute on the EditUser method, which ensures that only authenticated users can access this method.

The userId is now retrieved from the authenticated user's claims, rather than being passed in from the client. This prevents insecure direct object references, as the client can no longer supply an arbitrary user ID.

The method then checks if the authenticated user's ID matches the ID of the user to be modified. If they don't match, the method returns an Unauthorized response. This ensures that users can only modify their own information.

The HashPassword method is used to hash the user's password before it is stored in the database. This ensures that even if the database is compromised, the attacker won't be able to retrieve the user's plaintext password.

The currentUser.Password = HashPassword(user.Password); line replaces the previous line that stored the password in plaintext. This ensures that passwords are hashed before being stored in the database.

Finally, the await _context.SaveChangesAsync(); line saves the changes to the database.

References

• 286. Insecure object reference - Personal information