Phishing Api Keys in Buffalo with Basic Auth

Basic Authentication encodes a username and password with Base64 and transmits the credentials in an HTTP header on every request. Because the encoding is reversible and the header is easily inspected, sending static API keys this way exposes them to interception. In Buffalo applications, if routes or handlers rely on Basic Auth to gate endpoints that return API keys, and those keys are also stored in configuration or passed through query parameters, the attack surface expands. An attacker who can observe or manipulate traffic—such as through a compromised network, a proxy logging headers, or client-side code leaking the Authorization header—can harvest the credentials. Because the same credentials often identify privileged operations or administrative endpoints, the leaked key may enable broader access, aligning with common OWASP API Top 10 risks like Broken Object Level Authorization (BOLA) and Excessive Data Exposure.

When API keys are embedded in Buffalo controllers and exposed through endpoints that also use Basic Auth, phishing can occur via social engineering that tricks a user into visiting a malicious site that triggers authenticated requests. For example, an attacker might craft a link that calls a Buffalo route which responds with an API key in JSON. If the route relies on Basic Auth for access control but does not additionally validate the intent or origin of the request, the key can be exfiltrated through the response. MiddleBrick’s unauthenticated scan detects such endpoints by checking whether responses inadvertently expose sensitive identifiers or secrets, and by correlating spec definitions with runtime behavior to highlight mismatches in authorization design.

Furthermore, Buffalo applications that parse the Authorization header manually may inadvertently log it or include it in error messages, creating secondary channels for leakage. Logs that contain Basic Auth credentials become targets for phishing if an attacker gains access to them. The scanner’s checks for Data Exposure and Input Validation surface these risks by identifying routes that return sensitive fields without proper scoping, and by flagging endpoints that do not enforce strict parameter validation. Because API keys often function as bearer tokens, exposing them through a Basic Auth–protected endpoint effectively turns the key into a phishable artifact, especially when combined with weak transport protections or inconsistent use of TLS.

To reduce risk, avoid relying solely on Basic Auth to protect endpoints that return or manage API keys. Instead, use token-based access controls and ensure that sensitive data is never returned in responses that rely only on Basic Auth for authorization. The following examples show how to implement safer patterns in a Buffalo application.

• Do not expose API keys through endpoints that use only Basic Auth. Require a separate, short-lived token or session-based check before returning sensitive values.
• Ensure the Authorization header is never logged. Configure your logging pipeline to filter or redact credentials.
• Always enforce Transport Layer Security and validate the Origin header where relevant to mitigate certain phishing vectors.

Example: A Buffalo route that safely handles authentication without exposing an API key in the response body.

// controllers/api_keys_controller.ex
defmodule MyApp.ApiKeysController do
  use MyAppWeb, :controller

  # Require a session-based authentication check in addition to any header-based validation
  plug :require_authenticated_session when action in [:show]

  def show(conn, %{"id" => id}) do
    # Perform proper authorization scoped to the requester’s permissions
    with {:ok, api_key} <- ApiKeyService.get_for_user(conn.assigns.current_user, id) do
      # Return only metadata, never the raw key used for authentication
      json(conn, %{id: api_key.id, name: api_key.name, created_at: api_key.inserted_at})
    else
      _ -> send_resp(conn, :not_found, "Not found")
    end
  end

  defp require_authenticated_session(conn, _opts) do
    if confirmed_user_session?(conn) do
      conn
    else
      send_resp(conn, :unauthorized, "Session required")
      halt(conn)
    end
  end
end

defp confirmed_user_session_(conn) do
  # Check session store or token validation rather than relying on Basic Auth alone
  get_session(conn, :user_id) != nil
end

Example: Validating a request using Basic Auth for administrative actions while ensuring the key is never echoed back.

// controllers/admin_controller.ex
defmodule MyApp.AdminController do
  use MyAppWeb, :controller

  # Use a plug to validate credentials without logging the header
  plug :validate_basic_auth when action in [:run]

  def run(conn, params) do
    # Proceed only if additional context (e.g., IP allowlist, session) is satisfied
    if allowed?(conn) do
      # Perform action that may involve sensitive operations but does not return API keys
      json(conn, %{status: "ok"})
    else
      send_resp(conn, :forbidden, "Access denied")
    end
  end

  defp validate_basic_auth(conn, _opts) do
    case get_req_header(conn, "authorization") do
      ["Basic " <> encoded] ->
        case Base.decode64(encoded) do
          "admin:" <> _secret when allowed_ip?(conn) -> conn
          _ -> send_resp(conn, :unauthorized, "Bad credentials") |> halt()
        end
      _ ->
        send_resp(conn, :unauthorized, "Missing header") |> halt()
    end
  end

  defp allowed_ip_(conn) do
    # Apply additional network-level checks
    true # Replace with real IP validation logic
  end
end