fix(http): make Hackney trust the CAStore bundle

Hackney trusts its own certifi bundle, which still has the roots of the
compromised eMudhra intermediate CAs. Pass explicit ssl_options with the
CAStore bundle. Hackney drops all its TLS defaults when ssl_options are
given, so keep peer and hostname checks in the options.

changelog.d/hackney-castore.security

@@ -0,0 +1 @@
+Hackney now trusts only the CAStore certificate bundle instead of its outdated certifi bundle, which still trusted the compromised eMudhra intermediate CAs

lib/pleroma/http/adapter_helper/hackney.ex

@@ -28,6 +28,7 @@ defmodule Pleroma.HTTP.AdapterHelper.Hackney do
     |> add_scheme_opts(uri)
     |> maybe_add_with_body()
     |> Pleroma.HTTP.AdapterHelper.maybe_add_proxy(proxy)
+    |> Pleroma.HTTP.TLS.put_hackney_ssl_options()
   end
 
   defp add_scheme_opts(opts, _), do: opts

lib/pleroma/http/tls.ex

@@ -0,0 +1,35 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.HTTP.TLS do
+  @moduledoc """
+  TLS client options that trust the CAStore bundle.
+
+  Hackney otherwise trusts its own certifi bundle, and it drops all of its
+  default TLS options, including certificate checks, as soon as any
+  `ssl_options` are given.
+  """
+
+  @spec ssl_options(keyword()) :: keyword()
+  def ssl_options(overrides \\ []) do
+    Keyword.merge(
+      [
+        verify: :verify_peer,
+        cacertfile: CAStore.file_path(),
+        depth: 20,
+        customize_hostname_check: [match_fun: :public_key.pkix_verify_hostname_match_fun(:https)]
+      ],
+      overrides
+    )
+  end
+
+  @spec put_hackney_ssl_options(keyword()) :: keyword()
+  def put_hackney_ssl_options(opts) do
+    if opts[:insecure] do
+      opts
+    else
+      Keyword.put(opts, :ssl_options, ssl_options(Keyword.get(opts, :ssl_options, [])))
+    end
+  end
+end

lib/pleroma/reverse_proxy/client/hackney.ex

@@ -28,9 +28,9 @@ defmodule Pleroma.ReverseProxy.Client.Hackney do
   @impl true
   def request(method, url, headers, body, opts \\ []) do
     opts =
-      Keyword.put_new(opts, :path_encode_fun, fn path ->
-        path
-      end)
+      opts
+      |> Keyword.put_new(:path_encode_fun, fn path -> path end)
+      |> Pleroma.HTTP.TLS.put_hackney_ssl_options()
 
     if opts[:follow_redirect] != false do
       {_state, req_opts} = Access.get_and_update(opts, :follow_redirect, fn a -> {a, false} end)

test/pleroma/http/adapter_helper/hackney_test.exs

@@ -39,5 +39,20 @@ defmodule Pleroma.HTTP.AdapterHelper.HackneyTest do
       assert opts[:b] == 1
       refute Keyword.has_key?(opts, :proxy)
     end
+
+    test "trusts the CAStore bundle", %{uri: uri} do
+      opts = Hackney.options([], uri)
+
+      assert opts[:ssl_options] == Pleroma.HTTP.TLS.ssl_options()
+    end
+
+    test "keeps the CAStore bundle with configured ssl_options", %{uri: uri} do
+      clear_config([:http, :adapter], ssl_options: [versions: [:"tlsv1.2"]])
+
+      opts = Hackney.options([], uri)
+
+      assert opts[:ssl_options][:versions] == [:"tlsv1.2"]
+      assert opts[:ssl_options][:cacertfile] == CAStore.file_path()
+    end
   end
 end

test/pleroma/http/tls_test.exs

@@ -0,0 +1,47 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.HTTP.TLSTest do
+  use ExUnit.Case, async: true
+
+  alias Pleroma.HTTP.TLS
+
+  describe "ssl_options/1" do
+    test "verifies peers against the CAStore bundle" do
+      opts = TLS.ssl_options()
+
+      assert opts[:verify] == :verify_peer
+      assert opts[:cacertfile] == CAStore.file_path()
+      assert [match_fun: match_fun] = opts[:customize_hostname_check]
+      assert is_function(match_fun, 2)
+    end
+
+    test "keeps the CA bundle when other options are given" do
+      opts = TLS.ssl_options(versions: [:"tlsv1.2"])
+
+      assert opts[:versions] == [:"tlsv1.2"]
+      assert opts[:cacertfile] == CAStore.file_path()
+      assert opts[:verify] == :verify_peer
+    end
+  end
+
+  describe "put_hackney_ssl_options/1" do
+    test "adds the TLS options" do
+      opts = TLS.put_hackney_ssl_options(pool: :media)
+
+      assert opts[:pool] == :media
+      assert opts[:ssl_options] == TLS.ssl_options()
+    end
+
+    test "merges given ssl_options into the TLS options" do
+      opts = TLS.put_hackney_ssl_options(ssl_options: [versions: [:"tlsv1.2"]])
+
+      assert opts[:ssl_options] == TLS.ssl_options(versions: [:"tlsv1.2"])
+    end
+
+    test "leaves insecure requests alone" do
+      assert TLS.put_hackney_ssl_options(insecure: true) == [insecure: true]
+    end
+  end
+end