Cross Site Request Forgery in Buffalo with Basic Auth

Cross Site Request Forgery (CSRF) is an attack that tricks a victim into submitting an unwanted request on a web application where they are authenticated. In Buffalo, using HTTP Basic Authentication heightens the risk because credentials are often stored in cookies after the initial authentication handshake, making them accessible to malicious sites if secure practices are not followed.

When a Buffalo application uses Basic Auth, the browser typically caches the credentials and sends them automatically with requests to the same origin. If the application does not implement anti-CSRF protections, an attacker can craft a malicious page that issues requests to the authenticated endpoint. Because the browser includes the Basic Auth credentials automatically, the server may process the request as legitimate, leading to unauthorized actions such as changing account settings or performing transactions.

Basic Auth over non-HTTPS channels exacerbates the problem since credentials can be intercepted and reused. Even over HTTPS, relying solely on Basic Auth without CSRF tokens leaves a gap because the authentication state is tied to the origin and cookies rather than to a synchronized token mechanism. Attack vectors like malicious image tags or forms submitted via JavaScript can exploit this, especially if the application does not validate the Origin or Referer headers strictly.

In a Buffalo API that also exposes unauthenticated or weakly authenticated endpoints, CSRF can intersect with other checks such as BOLA/IDOR if the attacker can guess or iterate over resource identifiers. The framework does not automatically enforce CSRF protection for non-form requests, so developers must explicitly add safeguards for state-changing operations. This is particularly important for endpoints that modify data, where the impact of a successful CSRF attack is high.

middleBrick scans can detect missing CSRF protections and weak authentication combinations by analyzing the OpenAPI specification and runtime behavior, highlighting risks such as missing anti-forgery tokens and insufficient origin validation. The tool also checks for related issues like improper handling of credentials across origins, helping teams understand how CSRF might be chained with other weaknesses.

To mitigate CSRF in Buffalo when using Basic Auth, implement anti-CSRF tokens for all state-changing requests and avoid relying on automatic credential sending by browsers. Use secure, same-site cookies for session tokens if you move away from Basic Auth for UI interactions, and always enforce HTTPS.

Below are concrete code examples for a Buffalo application that uses Basic Auth for an API endpoint while adding CSRF protection for forms and AJAX requests.

Example 1: Secure Basic Auth setup with CSRF token validation

// app/controllers/api_controller.ex
defmodule MyApp.ApiController do
  use MyApp, :controller

  before_action :authenticate_basic_auth
  before_action :validate_csrf_token, only: [:update, :create, :delete]

  defp authenticate_basic_auth(conn, _opts) do
    case Plug.BasicAuth.parse_basic_auth(conn) do
      {username, password} when username == "admin" and password == "s3cret" ->
        conn
        |> put_session(:auth_type, :basic)
        |> assign(:current_user, username)
      _ ->
        conn
        |> put_resp_header("www-authenticate", "Basic realm=\"Secure Area\"")
        |> send_resp(401, "Unauthorized")
        |> halt()
    end
  end

  defp validate_csrf_token(conn, _opts) do
    token = get_session(conn, :csrf_token)
    provided = conn.params["_csrf_token"] || conn.req_headers["x-csrf-token"]
    if token == provided do
      conn
    else
      conn
      |> send_resp(403, "Invalid CSRF token")
      |> halt()
    end
  end

  def update(conn, %{"id" => id, "resource" => resource_params}) do
    # Business logic here
    json(conn, %{status: "updated", id: id})
  end
end

Example 2: Generating and embedding CSRF tokens in forms

// app/views/layout_view.ex
defmodule MyApp.LayoutView do
  use MyApp, :view

  def csrf_token_tag(conn) do
    token = Plug.CSRFProtection.get_token(conn)
    ~E"""
    
    """
  end
end

// In a template (e.g., edit.html.eex)

  <%= csrf_token_tag(@conn) %>
  
  Save

Example 3: AJAX requests with CSRF token header

// assets/js/app.js
function safeUpdate(url, data) {
  const token = document.querySelector('input[name="_csrf_token"]').value;
  return fetch(url, {
    method: 'PUT',
    headers: {
      'Content-Type': 'application/json',
      'X-CSRF-Token': token
    },
    body: JSON.stringify(data)
  });
}

For API-only consumers, consider using token-based authentication (e.g., Bearer tokens) instead of Basic Auth for UI-related endpoints, and enforce CORS and strict origin checks. The Pro plan of middleBrick includes continuous monitoring that can alert you if CSRF protections are missing or inconsistent across endpoints.