CommonAPI: Prevent users from accessing media of other users

changelog.d/check-attachment-attribution.security

@@ -0,0 +1 @@
+CommonAPI: Prevent users from accessing media of other users by creating a status with reused attachment ID

lib/pleroma/scheduled_activity.ex

@@ -40,7 +40,11 @@ defp with_media_attachments(
          %{changes: %{params: %{"media_ids" => media_ids} = params}} = changeset
        )
        when is_list(media_ids) do
-    media_attachments = Utils.attachments_from_ids(%{media_ids: media_ids})
+    media_attachments =
+      Utils.attachments_from_ids(
+        %{media_ids: media_ids},
+        User.get_cached_by_id(changeset.data.user_id)
+      )
 
     params =
       params

lib/pleroma/web/common_api.ex

@@ -33,6 +33,7 @@ def block(blocker, blocked) do
 
   def post_chat_message(%User{} = user, %User{} = recipient, content, opts \\ []) do
     with maybe_attachment <- opts[:media_id] && Object.get_by_id(opts[:media_id]),
+         :ok <- validate_chat_attachment_attribution(maybe_attachment, user),
          :ok <- validate_chat_content_length(content, !!maybe_attachment),
          {_, {:ok, chat_message_data, _meta}} <-
            {:build_object,
@@ -71,6 +72,17 @@ defp format_chat_content(content) do
     text
   end
 
+  defp validate_chat_attachment_attribution(nil, _), do: :ok
+
+  defp validate_chat_attachment_attribution(attachment, user) do
+    with :ok <- Object.authorize_access(attachment, user) do
+      :ok
+    else
+      e ->
+        e
+    end
+  end
+
   defp validate_chat_content_length(_, true), do: :ok
   defp validate_chat_content_length(nil, false), do: {:error, :no_content}
 

lib/pleroma/web/common_api/activity_draft.ex

@@ -111,7 +111,7 @@ defp full_payload(%{status: status, summary: summary} = draft) do
   end
 
   defp attachments(%{params: params} = draft) do
-    attachments = Utils.attachments_from_ids(params)
+    attachments = Utils.attachments_from_ids(params, draft.user)
     draft = %__MODULE__{draft | attachments: attachments}
 
     case Utils.validate_attachments_count(attachments) do

lib/pleroma/web/common_api/utils.ex

@@ -23,21 +23,21 @@ defmodule Pleroma.Web.CommonAPI.Utils do
   require Logger
   require Pleroma.Constants
 
-  def attachments_from_ids(%{media_ids: ids, descriptions: desc}) do
-    attachments_from_ids_descs(ids, desc)
+  def attachments_from_ids(%{media_ids: ids, descriptions: desc}, user) do
+    attachments_from_ids_descs(ids, desc, user)
   end
 
-  def attachments_from_ids(%{media_ids: ids}) do
-    attachments_from_ids_no_descs(ids)
+  def attachments_from_ids(%{media_ids: ids}, user) do
+    attachments_from_ids_no_descs(ids, user)
   end
 
-  def attachments_from_ids(_), do: []
+  def attachments_from_ids(_, _), do: []
 
-  def attachments_from_ids_no_descs([]), do: []
+  def attachments_from_ids_no_descs([], _), do: []
 
-  def attachments_from_ids_no_descs(ids) do
+  def attachments_from_ids_no_descs(ids, user) do
     Enum.map(ids, fn media_id ->
-      case get_attachment(media_id) do
+      case get_attachment(media_id, user) do
         %Object{data: data} -> data
         _ -> nil
       end
@@ -45,22 +45,23 @@ def attachments_from_ids_no_descs(ids) do
     |> Enum.reject(&is_nil/1)
   end
 
-  def attachments_from_ids_descs([], _), do: []
+  def attachments_from_ids_descs([], _, _), do: []
 
-  def attachments_from_ids_descs(ids, descs_str) do
+  def attachments_from_ids_descs(ids, descs_str, user) do
     {_, descs} = Jason.decode(descs_str)
 
     Enum.map(ids, fn media_id ->
-      with %Object{data: data} <- get_attachment(media_id) do
+      with %Object{data: data} <- get_attachment(media_id, user) do
         Map.put(data, "name", descs[media_id])
       end
     end)
     |> Enum.reject(&is_nil/1)
   end
 
-  defp get_attachment(media_id) do
+  defp get_attachment(media_id, user) do
     with %Object{data: data} = object <- Repo.get(Object, media_id),
-         %{"type" => type} when type in Pleroma.Constants.upload_object_types() <- data do
+         %{"type" => type} when type in Pleroma.Constants.upload_object_types() <- data,
+         :ok <- Object.authorize_access(object, user) do
       object
     else
       _ -> nil

test/pleroma/web/common_api/utils_test.exs

@@ -586,46 +586,61 @@ test "returns recipients when object not found" do
     end
   end
 
-  describe "attachments_from_ids_descs/2" do
+  describe "attachments_from_ids_descs/3" do
     test "returns [] when attachment ids is empty" do
-      assert Utils.attachments_from_ids_descs([], "{}") == []
+      assert Utils.attachments_from_ids_descs([], "{}", nil) == []
     end
 
     test "returns list attachments with desc" do
-      object = insert(:attachment)
+      user = insert(:user)
+      object = insert(:attachment, %{user: user})
       desc = Jason.encode!(%{object.id => "test-desc"})
 
-      assert Utils.attachments_from_ids_descs(["#{object.id}", "34"], desc) == [
+      assert Utils.attachments_from_ids_descs(["#{object.id}", "34"], desc, user) == [
                Map.merge(object.data, %{"name" => "test-desc"})
              ]
     end
   end
 
-  describe "attachments_from_ids/1" do
+  describe "attachments_from_ids/2" do
     test "returns attachments with descs" do
-      object = insert(:attachment)
+      user = insert(:user)
+      object = insert(:attachment, %{user: user})
       desc = Jason.encode!(%{object.id => "test-desc"})
 
-      assert Utils.attachments_from_ids(%{
-               media_ids: ["#{object.id}"],
-               descriptions: desc
-             }) == [
+      assert Utils.attachments_from_ids(
+               %{
+                 media_ids: ["#{object.id}"],
+                 descriptions: desc
+               },
+               user
+             ) == [
                Map.merge(object.data, %{"name" => "test-desc"})
              ]
     end
 
     test "returns attachments without descs" do
-      object = insert(:attachment)
-      assert Utils.attachments_from_ids(%{media_ids: ["#{object.id}"]}) == [object.data]
+      user = insert(:user)
+      object = insert(:attachment, %{user: user})
+      assert Utils.attachments_from_ids(%{media_ids: ["#{object.id}"]}, user) == [object.data]
     end
 
     test "returns [] when not pass media_ids" do
-      assert Utils.attachments_from_ids(%{}) == []
+      assert Utils.attachments_from_ids(%{}, nil) == []
+    end
+
+    test "returns [] when media_ids not belong to current user" do
+      user = insert(:user)
+      user2 = insert(:user)
+
+      object = insert(:attachment, %{user: user})
+
+      assert Utils.attachments_from_ids(%{media_ids: ["#{object.id}"]}, user2) == []
     end
 
     test "checks that the object is of upload type" do
       object = insert(:note)
-      assert Utils.attachments_from_ids(%{media_ids: ["#{object.id}"]}) == []
+      assert Utils.attachments_from_ids(%{media_ids: ["#{object.id}"]}, nil) == []
     end
   end
 

test/pleroma/web/common_api_test.exs

@@ -279,6 +279,24 @@ test "it reject messages via MRF" do
       assert {:reject, "[KeywordPolicy] Matches with rejected keyword"} ==
                CommonAPI.post_chat_message(author, recipient, "GNO/Linux")
     end
+
+    test "it reject messages with attachments not belonging to user" do
+      author = insert(:user)
+      not_author = insert(:user)
+      recipient = author
+
+      attachment = insert(:attachment, %{user: not_author})
+
+      {:error, message} =
+        CommonAPI.post_chat_message(
+          author,
+          recipient,
+          "123",
+          media_id: attachment.id
+        )
+
+      assert message == :forbidden
+    end
   end
 
   describe "unblocking" do

test/pleroma/web/mastodon_api/views/scheduled_activity_view_test.exs

@@ -48,7 +48,7 @@ test "A scheduled activity with a media attachment" do
       id: to_string(scheduled_activity.id),
       media_attachments:
         %{media_ids: [upload.id]}
-        |> Utils.attachments_from_ids()
+        |> Utils.attachments_from_ids(user)
         |> Enum.map(&StatusView.render("attachment.json", %{attachment: &1})),
       params: %{
         in_reply_to_id: to_string(activity.id),

test/pleroma/web/pleroma_api/views/chat_message_reference_view_test.exs

@@ -24,7 +24,7 @@ test "it displays a chat message" do
       filename: "an_image.jpg"
     }
 
-    {:ok, upload} = ActivityPub.upload(file, actor: user.ap_id)
+    {:ok, upload} = ActivityPub.upload(file, actor: recipient.ap_id)
 
     {:ok, activity} =
       CommonAPI.post_chat_message(user, recipient, "kippis :firefox:", idempotency_key: "123")