From 38bcf6b19e3d83cb6c4e6c82d237a26edcab167a Mon Sep 17 00:00:00 2001
From: Mark Felder <feld@feld.me>
Date: Fri, 26 May 2023 12:08:50 -0400
Subject: [PATCH] MediaProxyController: Apply CSP sandbox

---
 changelog.d/3126.fix                             |  1 +
 .../web/media_proxy/media_proxy_controller.ex    |  7 +++++++
 .../media_proxy/media_proxy_controller_test.exs  | 16 ++++++++++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 changelog.d/3126.fix

diff --git a/changelog.d/3126.fix b/changelog.d/3126.fix
new file mode 100644
index 000000000..91d396c89
--- /dev/null
+++ b/changelog.d/3126.fix
@@ -0,0 +1 @@
+MediaProxy responses now return a sandbox CSP header
diff --git a/lib/pleroma/web/media_proxy/media_proxy_controller.ex b/lib/pleroma/web/media_proxy/media_proxy_controller.ex
index d2ad62c13..bda5b36ed 100644
--- a/lib/pleroma/web/media_proxy/media_proxy_controller.ex
+++ b/lib/pleroma/web/media_proxy/media_proxy_controller.ex
@@ -12,6 +12,8 @@ defmodule Pleroma.Web.MediaProxy.MediaProxyController do
   alias Pleroma.Web.MediaProxy
   alias Plug.Conn
 
+  plug(:sandbox)
+
   def remote(conn, %{"sig" => sig64, "url" => url64}) do
     with {_, true} <- {:enabled, MediaProxy.enabled?()},
          {:ok, url} <- MediaProxy.decode_url(sig64, url64),
@@ -202,4 +204,9 @@ defmodule Pleroma.Web.MediaProxy.MediaProxyController do
   defp media_proxy_opts do
     Config.get([:media_proxy, :proxy_opts], [])
   end
+
+  defp sandbox(conn, _params) do
+    conn
+    |> merge_resp_headers([{"content-security-policy", "sandbox;"}])
+  end
 end
diff --git a/test/pleroma/web/media_proxy/media_proxy_controller_test.exs b/test/pleroma/web/media_proxy/media_proxy_controller_test.exs
index 5246bf0c4..9ce092fd8 100644
--- a/test/pleroma/web/media_proxy/media_proxy_controller_test.exs
+++ b/test/pleroma/web/media_proxy/media_proxy_controller_test.exs
@@ -6,7 +6,9 @@ defmodule Pleroma.Web.MediaProxy.MediaProxyControllerTest do
   use Pleroma.Web.ConnCase
 
   import Mock
+  import Mox
 
+  alias Pleroma.ReverseProxy.ClientMock
   alias Pleroma.Web.MediaProxy
   alias Plug.Conn
 
@@ -74,6 +76,20 @@ defmodule Pleroma.Web.MediaProxy.MediaProxyControllerTest do
         assert %Conn{status: 404, resp_body: "Not Found"} = get(conn, url)
       end
     end
+
+    test "it applies sandbox CSP to MediaProxy requests", %{conn: conn} do
+      media_url = "https://lain.com/image.png"
+      media_proxy_url = MediaProxy.encode_url(media_url)
+
+      ClientMock
+      |> expect(:request, fn :get, ^media_url, _, _, _ ->
+        {:ok, 200, [{"content-type", "image/png"}]}
+      end)
+
+      %Conn{resp_headers: headers} = get(conn, media_proxy_url)
+
+      assert {"content-security-policy", "sandbox;"} in headers
+    end
   end
 
   describe "Media Preview Proxy" do