lib/pleroma/object/containment.ex

@@ -101,4 +101,12 @@ def contain_child(%{"object" => %{"id" => id, "attributedTo" => _} = object}),
     do: contain_origin(id, object)
 
   def contain_child(_), do: :ok
+
+  @doc "Checks whether two URIs belong to the same domain"
+  def same_origin(id1, id2) do
+    uri1 = URI.parse(id1)
+    uri2 = URI.parse(id2)
+
+    compare_uris(uri1, uri2)
+  end
 end

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -22,6 +22,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
   alias Pleroma.Upload
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.MRF
+  alias Pleroma.Web.ActivityPub.ObjectValidators.UserValidator
   alias Pleroma.Web.ActivityPub.Transmogrifier
   alias Pleroma.Web.Streamer
   alias Pleroma.Web.WebFinger
@@ -1722,6 +1723,7 @@ def user_data_from_user_object(data, additional \\ []) do
 
   def fetch_and_prepare_user_from_ap_id(ap_id, additional \\ []) do
     with {:ok, data} <- Fetcher.fetch_and_contain_remote_object_from_id(ap_id),
+         {:valid, {:ok, _, _}} <- {:valid, UserValidator.validate(data, [])},
          {:ok, data} <- user_data_from_user_object(data, additional) do
       {:ok, maybe_update_follow_information(data)}
     else
@@ -1734,6 +1736,10 @@ def fetch_and_prepare_user_from_ap_id(ap_id, additional \\ []) do
         Logger.debug("Rejected user #{ap_id}: #{inspect(reason)}")
         {:error, e}
 
+      {:valid, reason} ->
+        Logger.debug("Data is not a valid user #{ap_id}: #{inspect(reason)}")
+        {:error, "Not a user"}
+
       {:error, e} ->
         Logger.error("Could not decode user at fetch #{ap_id}, #{inspect(e)}")
         {:error, e}

lib/pleroma/web/activity_pub/object_validators/user_validator.ex

@@ -0,0 +1,92 @@
+# Akkoma: Magically expressive social media
+# Copyright © 2024 Akkoma Authors <https://akkoma.dev/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.ObjectValidators.UserValidator do
+  @moduledoc """
+  Checks whether ActivityPub data represents a valid user
+
+  Users don't go through the same ingest pipeline like activities or other objects.
+  To ensure this can only match a user and no users match in the other pipeline,
+  this is a separate from the generic ObjectValidator.
+  """
+
+  @behaviour Pleroma.Web.ActivityPub.ObjectValidator.Validating
+
+  alias Pleroma.Object.Containment
+  alias Pleroma.Signature
+
+  @impl true
+  def validate(object, meta)
+
+  def validate(%{"type" => type, "id" => _id} = data, meta)
+      when type in ["Person", "Organization", "Group", "Application"] do
+    with :ok <- validate_pubkey(data),
+         :ok <- validate_inbox(data),
+         :ok <- contain_collection_origin(data) do
+      {:ok, data, meta}
+    else
+      {:error, e} -> {:error, e}
+      e -> {:error, e}
+    end
+  end
+
+  def validate(_, _), do: {:error, "Not a user object"}
+
+  defp mabye_validate_owner(nil, _actor), do: :ok
+  defp mabye_validate_owner(actor, actor), do: :ok
+  defp mabye_validate_owner(_owner, _actor), do: :error
+
+  defp validate_pubkey(
+         %{"id" => id, "publicKey" => %{"id" => pk_id, "publicKeyPem" => _key}} = data
+       )
+       when id != nil do
+    with {_, {:ok, kactor}} <- {:key, Signature.key_id_to_actor_id(pk_id)},
+         true <- id == kactor,
+         :ok <- mabye_validate_owner(Map.get(data, "owner"), id) do
+      :ok
+    else
+      {:key, _} ->
+        {:error, "Unable to determine actor id from key id"}
+
+      false ->
+        {:error, "Key id does not relate to user id"}
+
+      _ ->
+        {:error, "Actor does not own its public key"}
+    end
+  end
+
+  # pubkey is optional atm
+  defp validate_pubkey(_data), do: :ok
+
+  defp validate_inbox(%{"id" => id, "inbox" => inbox}) do
+    case Containment.same_origin(id, inbox) do
+      :ok -> :ok
+      :error -> {:error, "Inbox on different doamin"}
+    end
+  end
+
+  defp validate_inbox(_), do: {:error, "No inbox"}
+
+  defp check_field_value(%{"id" => id} = _data, value) do
+    Containment.same_origin(id, value)
+  end
+
+  defp maybe_check_field(data, field) do
+    with val when val != nil <- data[field],
+         :ok <- check_field_value(data, val) do
+      :ok
+    else
+      nil -> :ok
+      _ -> {:error, "#{field} on different domain"}
+    end
+  end
+
+  defp contain_collection_origin(data) do
+    Enum.reduce(["followers", "following", "featured"], :ok, fn
+      field, :ok -> maybe_check_field(data, field)
+      _, error -> error
+    end)
+  end
+end

test/fixtures/bridgy/actor.json

@@ -70,7 +70,7 @@
   "preferredUsername": "jk.nipponalba.scot",
   "summary": "",
   "publicKey": {
-    "id": "jk.nipponalba.scot",
+    "id": "https://fed.brid.gy/jk.nipponalba.scot#key",
     "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDdarxwzxnNbJ2hneWOYHkYJowk\npyigQtxlUd0VjgSQHwxU9kWqfbrHBVADyTtcqi/4dAzQd3UnCI1TPNnn4LPZY9PW\noiWd3Zl1/EfLFxO7LU9GS7fcSLQkyj5JNhSlN3I8QPudZbybrgRDVZYooDe1D+52\n5KLGqC2ajrIVOiDRTQIDAQAB\n-----END PUBLIC KEY-----"
   },
   "inbox": "https://fed.brid.gy/jk.nipponalba.scot/inbox",

test/fixtures/tesla_mock/https___osada.macgirvin.com_channel_mike.json

@@ -37,7 +37,7 @@
         "sharedInbox": "https://osada.macgirvin.com/inbox"
     },
     "publicKey": {
-        "id": "https://osada.macgirvin.com/channel/mike/public_key_pem",
+        "id": "https://osada.macgirvin.com/channel/mike",
         "owner": "https://osada.macgirvin.com/channel/mike",
         "publicKeyPem": "-----BEGIN PUBLIC KEY-----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\nnJhQF8udPLcXLaj6GW75JacCAwEAAQ==\n-----END PUBLIC KEY-----\n"
     },

test/fixtures/tesla_mock/kaniini@hubzilla.example.org.json

@@ -1 +1 @@
-{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1","https://hubzilla.example.org/apschema/v1.2"],"type":"Person","id":"https://hubzilla.example.org/channel/kaniini","preferredUsername":"kaniini","name":"kaniini","icon":{"type":"Image","mediaType":"image/jpeg","url":"https://hubzilla.example.org/photo/profile/l/281","height":300,"width":300},"url":{"type":"Link","mediaType":"text/html","href":"https://hubzilla.example.org/channel/kaniini"},"inbox":"https://hubzilla.example.org/inbox/kaniini","outbox":"https://hubzilla.example.org/outbox/kaniini","followers":"https://hubzilla.example.org/followers/kaniini","following":"https://hubzilla.example.org/following/kaniini","endpoints":{"sharedInbox":"https://hubzilla.example.org/inbox"},"publicKey":{"id":"https://hubzilla.example.org/channel/kaniini/public_key_pem","owner":"https://hubzilla.example.org/channel/kaniini","publicKeyPem":"-----BEGIN PUBLIC KEY-----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\nDropXWaOfy7Lac+G4qlfSgsCAwEAAQ==\n-----END PUBLIC KEY-----\n"},"nomadicLocations":[{"id":"https://hubzilla.example.org/locs/kaniini","type":"nomadicLocation","locationAddress":"acct:kaniini@hubzilla.example.org","locationPrimary":true,"locationDeleted":false}],"signature":{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1"],"type":"RsaSignature2017","nonce":"6b981a2f3bdcffc20252e3b131d4a4569fd2dea9fac543e5196136302f492694","creator":"https://hubzilla.example.org/channel/kaniini/public_key_pem","created":"2018-05-19T08:19:13Z","signatureValue":"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"}}
+{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1","https://hubzilla.example.org/apschema/v1.2"],"type":"Person","id":"https://hubzilla.example.org/channel/kaniini","preferredUsername":"kaniini","name":"kaniini","icon":{"type":"Image","mediaType":"image/jpeg","url":"https://hubzilla.example.org/photo/profile/l/281","height":300,"width":300},"url":{"type":"Link","mediaType":"text/html","href":"https://hubzilla.example.org/channel/kaniini"},"inbox":"https://hubzilla.example.org/inbox/kaniini","outbox":"https://hubzilla.example.org/outbox/kaniini","followers":"https://hubzilla.example.org/followers/kaniini","following":"https://hubzilla.example.org/following/kaniini","endpoints":{"sharedInbox":"https://hubzilla.example.org/inbox"},"publicKey":{"id":"https://hubzilla.example.org/channel/kaniini","owner":"https://hubzilla.example.org/channel/kaniini","publicKeyPem":"-----BEGIN PUBLIC KEY-----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\nDropXWaOfy7Lac+G4qlfSgsCAwEAAQ==\n-----END PUBLIC KEY-----\n"},"nomadicLocations":[{"id":"https://hubzilla.example.org/locs/kaniini","type":"nomadicLocation","locationAddress":"acct:kaniini@hubzilla.example.org","locationPrimary":true,"locationDeleted":false}],"signature":{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1"],"type":"RsaSignature2017","nonce":"6b981a2f3bdcffc20252e3b131d4a4569fd2dea9fac543e5196136302f492694","creator":"https://hubzilla.example.org/channel","created":"2018-05-19T08:19:13Z","signatureValue":"ezpT4iCIUzJSeJa/Jsf4EkgbX9enWZG/0eliLXZcvkeCX9mZabaX9LMQRViP2GSlAJBHJu+UqK5LWaoWw9pYkQQHUL+43w2DeBxQicEcPqpT46j6pHuWptfwB8YHTC2/Pb56Y/jseU37j+FW8xVmcGZk4cPqJRLQNojwJlQiFOpBEd4Cel6081W12Pep578+6xBL+h92RJsWznA1gE/NV9dkCqoAoNdiORJg68sVTm0yYxPit2D/DLwXUFeBhC47EZtY3DtAOf7rADGwbquXKug/wtEI47R4p9dJvMWERSVW9O2FmDk8deUjRR3qO1iYGce8O+uMnnBHmuTcToRUHH7mxfMdqjfbcZ9DGBjKtLPSOyVPT9rENeyX8fsksmX0XhfHsNSWkmeDaU5/Au3IY75gDewiGzmzLOpRc6GUnHHro7lMpyMuo3lLZKjNVsFZbx+sXCYwORz5GAMuwIt/iCUdrsQsF5aycqfUAZrFBPguH6DVjbMUqyLvS78sDKiWqgWVhq9VDKse+WuQaJLGBDJNF9APoA6NDMjjIBZfmkGf2mV7ubIYihoOncUjahFqxU5306cNxAcdj2uNcwkgX4BCnBe/L2YsvMHhZrupzDewWWy4fxhktyoZ7VhLSl1I7fMPytjOpb9EIvng4DHGX2t+hKfon2rCGfECPavwiTM="}}