5 files changed, 58 insertions, 0 deletions
diff --git a/lib/pleroma/web/activity_pub/activity_pub.ex b/lib/pleroma/web/activity_pub/activity_pub.ex
index e6c2dc9cf..81c11dd76 100644
--- a/lib/pleroma/web/activity_pub/activity_pub.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub.ex
@@ -747,6 +747,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
              "actor" => data["attributedTo"],
              "object" => data
            },
+           :ok <- Transmogrifier.contain_origin(id, params),
            {:ok, activity} <- Transmogrifier.handle_incoming(params) do
         {:ok, Object.normalize(activity.data["object"])}
       else
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 1367bc7e3..4a3a82195 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -31,6 +31,20 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   end
 
   @doc """
+  Checks that an imported AP object's actor matches the domain it came from.
+  """
+  def contain_origin(id, %{"actor" => actor} = params) do
+    id_uri = URI.parse(id)
+    actor_uri = URI.parse(get_actor(params))
+
+    if id_uri.host == actor_uri.host do
+      :ok
+    else
+      :error
+    end
+  end
+
+  @doc """
   Modifies an incoming AP object (mastodon format) to our internal format.
   """
   def fix_object(object) do
diff --git a/test/fixtures/httpoison_mock/https__info.pleroma.site_activity.json b/test/fixtures/httpoison_mock/https__info.pleroma.site_activity.json
new file mode 100644
index 000000000..eab0341fe
--- /dev/null
+++ b/test/fixtures/httpoison_mock/https__info.pleroma.site_activity.json
@@ -0,0 +1,14 @@
+{
+        "@context": "https://www.w3.org/ns/activitystreams",
+        "actor": "https://mastodon.example.org/users/admin",
+        "attachment": [],
+        "attributedTo": "https://mastodon.example.org/users/admin",
+        "content": "<p>this post was not actually written by Haelwenn</p>",
+        "id": "https://info.pleroma.site/activity.json",
+        "published": "2018-09-01T22:15:00Z",
+        "tag": [],
+        "to": [
+            "https://www.w3.org/ns/activitystreams#Public"
+        ],
+        "type": "Note"
+}
diff --git a/test/support/httpoison_mock.ex b/test/support/httpoison_mock.ex
index 4ee2feb95..7057f30fb 100644
--- a/test/support/httpoison_mock.ex
+++ b/test/support/httpoison_mock.ex
@@ -3,6 +3,14 @@ defmodule HTTPoisonMock do
 
   def get(url, body \\ [], headers \\ [])
 
+  def get("https://info.pleroma.site/activity.json", _, _) do
+    {:ok,
+     %Response{
+       status_code: 200,
+       body: File.read!("test/fixtures/httpoison_mock/https__info.pleroma.site_activity.json")
+     }}
+  end
+
   def get("https://puckipedia.com/", [Accept: "application/activity+json"], _) do
     {:ok,
      %Response{
diff --git a/test/web/activity_pub/transmogrifier_test.exs b/test/web/activity_pub/transmogrifier_test.exs
index e2926d495..afa25bb60 100644
--- a/test/web/activity_pub/transmogrifier_test.exs
+++ b/test/web/activity_pub/transmogrifier_test.exs
@@ -798,4 +798,25 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       assert rewritten["url"] == "http://example.com"
     end
   end
+
+  describe "actor origin containment" do
+    test "it rejects objects with a bogus origin" do
+      {:error, _} = ActivityPub.fetch_object_from_id("https://info.pleroma.site/activity.json")
+    end
+
+    test "it rejects activities which reference objects with bogus origins" do
+      user = insert(:user, %{local: false})
+
+      data = %{
+        "@context" => "https://www.w3.org/ns/activitystreams",
+        "id" => user.ap_id <> "/activities/1234",
+        "actor" => user.ap_id,
+        "to" => ["https://www.w3.org/ns/activitystreams#Public"],
+        "object" => "https://info.pleroma.site/activity.json",
+        "type" => "Announce"
+      }
+
+      :error = Transmogrifier.handle_incoming(data)
+    end
+  end
 end