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Privilege escalation

Need​

Enhancement of role-based access control to prevent unauthorized privilege escalation

Context​

  • Usage of C# 7.0 for modern language features and enhancements
  • 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

Description​

Non compliant code​

public class UserController : Controller
{
    private readonly UserManager<IdentityUser> _userManager;

    public UserController(UserManager<IdentityUser> userManager)
    {
        _userManager = userManager;
    }

    [HttpPost]
    public async Task<IActionResult> UpgradeUserToAdmin(string userId)
    {
        var user = await _userManager.FindByIdAsync(userId);
        await _userManager.AddToRoleAsync(user, "Admin");
        return Ok();
    }
}

In the code above, the UserController class has an UpgradeUserToAdmin method which is accessible via HTTP POST request. This method is intended to upgrade a user to an admin role.

The problem here is that there are no checks in place to ensure that the user making the request has the necessary permissions to perform this action. As a result, any user, even those with standard user privileges, can send a POST request to this endpoint and upgrade any user (including themselves) to an admin role.

This is a classic example of a Privilege Escalation vulnerability, where a less privileged user gains elevated access to resources that are normally protected from an application or system. In this case, a standard user can gain administrative privileges, which could lead to unauthorized access to sensitive data or unauthorized actions.

Steps​

  • Implement proper authorization and authentication mechanisms in the application.
  • Ensure that only authorized users have access to the 'UpgradeUserToAdmin' endpoint.
  • Use role-based access control (RBAC) to restrict access to administrative functionality.
  • Validate the user's authorization level before allowing them to upgrade to an admin role.
  • Implement least privilege principle by granting only necessary permissions to users.
  • Regularly review and update role configurations to ensure they are secure and up-to-date.
  • Consider implementing multi-factor authentication for administrative accounts.
  • Conduct regular security audits and penetration testing to identify and address any vulnerabilities.

Compliant code​

[Authorize(Roles = "Admin")]
[HttpPost]
public async Task<IActionResult> UpgradeUserToAdmin(string userId)
{
    var currentUser = await _userManager.GetUserAsync(User);
    if (currentUser == null || !await _userManager.IsInRoleAsync(currentUser, "Admin"))
    {
        return Unauthorized();
    }

    var user = await _userManager.FindByIdAsync(userId);
    if (user == null)
    {
        return NotFound();
    }

    await _userManager.AddToRoleAsync(user, "Admin");
    return Ok();
}

The updated code now includes an [Authorize(Roles = "Admin")] attribute on the UpgradeUserToAdmin method. This attribute ensures that only users who are already in the "Admin" role can access this method.

In addition, the code now checks if the current user is in the "Admin" role before allowing them to upgrade another user to an admin role. If the current user is not an admin, the method returns an Unauthorized status code.

The code also checks if the user to be upgraded exists. If the user does not exist, the method returns a NotFound status code.

This updated code helps prevent privilege escalation by ensuring that only authorized users can upgrade other users to an admin role. It also implements the principle of least privilege by granting only necessary permissions to users.

Remember to regularly review and update role configurations to ensure they are secure and up-to-date. Consider implementing multi-factor authentication for administrative accounts and conduct regular security audits and penetration testing to identify and address any vulnerabilities.

References​

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