pleroma

http_security_plug.ex (8500B)

# Pleroma: A lightweight social networking server
# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
# SPDX-License-Identifier: AGPL-3.0-only
defmodule Pleroma.Web.Plugs.HTTPSecurityPlug do
  import Plug.Conn
  require Logger
  @config_impl Application.compile_env(:pleroma, [__MODULE__, :config_impl], Pleroma.Config)
  def init(opts), do: opts
  def call(conn, _options) do
    if @config_impl.get([:http_security, :enabled]) do
      conn
      |> merge_resp_headers(headers())
      |> maybe_send_sts_header(@config_impl.get([:http_security, :sts]))
    else
      conn
    end
  end
  def primary_frontend do
    with %{"name" => frontend} <- @config_impl.get([:frontends, :primary]),
         available <- @config_impl.get([:frontends, :available]),
         %{} = primary_frontend <- Map.get(available, frontend) do
      {:ok, primary_frontend}
    end
  end
  def custom_http_frontend_headers do
    with {:ok, %{"custom-http-headers" => custom_headers}} <- primary_frontend() do
      custom_headers
    else
      _ -> []
    end
  end
  def headers do
    referrer_policy = @config_impl.get([:http_security, :referrer_policy])
    report_uri = @config_impl.get([:http_security, :report_uri])
    custom_http_frontend_headers = custom_http_frontend_headers()
    headers = [
      {"x-xss-protection", "1; mode=block"},
      {"x-permitted-cross-domain-policies", "none"},
      {"x-frame-options", "DENY"},
      {"x-content-type-options", "nosniff"},
      {"referrer-policy", referrer_policy},
      {"x-download-options", "noopen"},
      {"content-security-policy", csp_string()},
      {"permissions-policy", "interest-cohort=()"}
    ]
    headers =
      if custom_http_frontend_headers do
        custom_http_frontend_headers ++ headers
      else
        headers
      end
    if report_uri do
      report_group = %{
        "group" => "csp-endpoint",
        "max-age" => 10_886_400,
        "endpoints" => [
          %{"url" => report_uri}
        ]
      }
      [{"report-to", Jason.encode!(report_group)} | headers]
    else
      headers
    end
  end
  static_csp_rules = [
    "default-src 'none'",
    "base-uri 'self'",
    "frame-ancestors 'none'",
    "style-src 'self' 'unsafe-inline'",
    "font-src 'self'",
    "manifest-src 'self'"
  ]
  @csp_start [Enum.join(static_csp_rules, ";") <> ";"]
  defp csp_string do
    scheme = @config_impl.get([Pleroma.Web.Endpoint, :url])[:scheme]
    static_url = Pleroma.Web.Endpoint.static_url()
    websocket_url = Pleroma.Web.Endpoint.websocket_url()
    report_uri = @config_impl.get([:http_security, :report_uri])
    img_src = "img-src 'self' data: blob:"
    media_src = "media-src 'self'"
    connect_src = ["connect-src 'self' blob: ", static_url, ?\s, websocket_url]
    # Strict multimedia CSP enforcement only when MediaProxy is enabled
    {img_src, media_src, connect_src} =
      if @config_impl.get([:media_proxy, :enabled]) &&
           !@config_impl.get([:media_proxy, :proxy_opts, :redirect_on_failure]) do
        sources = build_csp_multimedia_source_list()
        {
          [img_src, sources],
          [media_src, sources],
          [connect_src, sources]
        }
      else
        {
          [img_src, " https:"],
          [media_src, " https:"],
          [connect_src, " https:"]
        }
      end
    connect_src =
      if @config_impl.get([:env]) == :dev do
        [connect_src, " http://localhost:3035/"]
      else
        connect_src
      end
    script_src =
      if @config_impl.get([:http_security, :allow_unsafe_eval]) do
        if @config_impl.get([:env]) == :dev do
          "script-src 'self' 'unsafe-eval'"
        else
          "script-src 'self' 'wasm-unsafe-eval'"
        end
      else
        "script-src 'self'"
      end
    report = if report_uri, do: ["report-uri ", report_uri, ";report-to csp-endpoint"]
    insecure = if scheme == "https", do: "upgrade-insecure-requests"
    @csp_start
    |> add_csp_param(img_src)
    |> add_csp_param(media_src)
    |> add_csp_param(connect_src)
    |> add_csp_param(script_src)
    |> add_csp_param(insecure)
    |> add_csp_param(report)
    |> :erlang.iolist_to_binary()
  end
  defp build_csp_from_whitelist([], acc), do: acc
  defp build_csp_from_whitelist([last], acc) do
    [build_csp_param_from_whitelist(last) | acc]
  end
  defp build_csp_from_whitelist([head | tail], acc) do
    build_csp_from_whitelist(tail, [[?\s, build_csp_param_from_whitelist(head)] | acc])
  end
  # TODO: use `build_csp_param/1` after removing support bare domains for media proxy whitelist
  defp build_csp_param_from_whitelist("http" <> _ = url) do
    build_csp_param(url)
  end
  defp build_csp_param_from_whitelist(url), do: url
  defp build_csp_multimedia_source_list do
    media_proxy_whitelist =
      [:media_proxy, :whitelist]
      |> @config_impl.get()
      |> build_csp_from_whitelist([])
    captcha_method = @config_impl.get([Pleroma.Captcha, :method])
    captcha_endpoint = @config_impl.get([captcha_method, :endpoint])
    base_endpoints =
      [
        [:media_proxy, :base_url],
        [Pleroma.Upload, :base_url],
        [Pleroma.Uploaders.S3, :public_endpoint]
      ]
      |> Enum.map(&@config_impl.get/1)
    [captcha_endpoint | base_endpoints]
    |> Enum.map(&build_csp_param/1)
    |> Enum.reduce([], &add_source(&2, &1))
    |> add_source(media_proxy_whitelist)
  end
  defp add_source(iodata, nil), do: iodata
  defp add_source(iodata, []), do: iodata
  defp add_source(iodata, source), do: [[?\s, source] | iodata]
  defp add_csp_param(csp_iodata, nil), do: csp_iodata
  defp add_csp_param(csp_iodata, param), do: [[param, ?;] | csp_iodata]
  defp build_csp_param(nil), do: nil
  defp build_csp_param(url) when is_binary(url) do
    %{host: host, scheme: scheme} = URI.parse(url)
    if scheme do
      [scheme, "://", host]
    end
  end
  def warn_if_disabled do
    unless Pleroma.Config.get([:http_security, :enabled]) do
      Logger.warning("
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HTTP Security is disabled. Please re-enable it to prevent users from attacking
your instance and your users via malicious posts:
      config :pleroma, :http_security, enabled: true
      ")
    end
  end
  defp maybe_send_sts_header(conn, true) do
    max_age_sts = @config_impl.get([:http_security, :sts_max_age])
    max_age_ct = @config_impl.get([:http_security, :ct_max_age])
    merge_resp_headers(conn, [
      {"strict-transport-security", "max-age=#{max_age_sts}; includeSubDomains"},
      {"expect-ct", "enforce, max-age=#{max_age_ct}"}
    ])
  end
  defp maybe_send_sts_header(conn, _), do: conn
end