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fix(fetcher): require fetched documents to have the fetched id

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The fetcher accepted any document whose id was on the same host as the
fetch URL. Anyone who can place a JSON file on a host, for example
through an upload, could pass it off as another object or actor from
that host.

The id of a fetched document must now be the URL it came from (after
redirects), ignoring a trailing slash, the fragment, the host case and
differences that our URL encoding removes.
If it differs, as for Mastodon's /@user/123 display URLs, we refetch
once from that id, which must be on the same host. The refetch must
not redirect and must match exactly.

Test mocks that served a document under a different URL now serve it
from its own id.

Based on Akkoma 8684964c5 and 940792f8b.
This commit is contained in:
Lain Soykaf 2026-10-27 21:45:14 +04:00
commit 20354e0aee
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8 changed files with 259 additions and 15 deletions
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34
test/pleroma/object/containment_test.exs
View file

@ -127,4 +127,38 @@ defmodule Pleroma.Object.ContainmentTest do
:ok = Containment.contain_child(data)
end
end
describe "contain_id_to_fetch/2" do
test "matches the exact id" do
assert :ok =
Containment.contain_id_to_fetch("https://a.test/o/1", %{
"id" => "https://a.test/o/1"
})
end
test "ignores fragments, a trailing slash and the host case" do
assert :ok =
Containment.contain_id_to_fetch("https://A.test/o/1/", %{
"id" => "https://a.test/o/1#x"
})
end
test "rejects another id on the same host" do
assert :error =
Containment.contain_id_to_fetch("https://a.test/o/1", %{
"id" => "https://a.test/o/2"
})
end
test "rejects a different query" do
assert :error =
Containment.contain_id_to_fetch("https://a.test/o?page=1", %{
"id" => "https://a.test/o?page=2"
})
end
test "rejects documents without an id" do
assert :error = Containment.contain_id_to_fetch("https://a.test/o/1", %{})
end
end
end

154
test/pleroma/object/fetcher_test.exs
View file

@ -48,6 +48,8 @@ defmodule Pleroma.Object.FetcherTest do
%{method: :get, url: "https://social.sakamoto.gq/notice/9wTkLEnuq47B25EehM"} ->
%Tesla.Env{
status: 200,
# Pleroma redirects /notice/:id to the object id
url: "https://social.sakamoto.gq/objects/f20f2497-66d9-4a52-a2e1-1be2a39c32c1",
body: File.read!("test/fixtures/fetch_mocks/9wTkLEnuq47B25EehM.json"),
headers: HttpRequestMock.activitypub_object_headers()
}
@ -642,7 +644,23 @@ defmodule Pleroma.Object.FetcherTest do
})
}
# No redirect - same domain
# Same-domain redirect to the object id
%{method: :get, url: "https://original.test/@actor/redirect"} ->
%Tesla.Env{
status: 200,
url: "https://original.test/objects/redirect-target",
headers: [{"content-type", "application/activity+json"}],
body:
Jason.encode!(%{
"id" => "https://original.test/objects/redirect-target",
"type" => "Note",
"content" => "This has a same-domain redirect",
"actor" => "https://original.test/users/actor",
"attributedTo" => "https://original.test/users/actor"
})
}
# Same-domain redirect to a document claiming the original URL as id
%{method: :get, url: "https://original.test/objects/same-domain-redirect"} ->
%Tesla.Env{
status: 200,
@ -695,12 +713,19 @@ defmodule Pleroma.Object.FetcherTest do
test "it accepts objects with same-domain redirects" do
assert {:ok, data} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://original.test/objects/same-domain-redirect"
"https://original.test/@actor/redirect"
)
assert data["content"] == "This has a same-domain redirect"
end
test "it rejects redirect targets that claim the original URL as id" do
assert {:error, _} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://original.test/objects/same-domain-redirect"
)
end
test "it handles responses without URL field (common in tests)" do
assert {:ok, data} =
Fetcher.fetch_and_contain_remote_object_from_id(
@ -711,6 +736,131 @@ defmodule Pleroma.Object.FetcherTest do
end
end
describe "id containment" do
setup do
note = fn id, content ->
%Tesla.Env{
status: 200,
headers: [{"content-type", "application/activity+json"}],
body:
Jason.encode!(%{
"id" => id,
"type" => "Note",
"content" => content,
"actor" => "https://host.test/users/actor",
"attributedTo" => "https://host.test/users/actor"
})
}
end
mock(fn
# display URL serving the canonical object
%{method: :get, url: "https://host.test/@actor/1"} ->
note.("https://host.test/objects/1", "display")
%{method: :get, url: "https://host.test/objects/1"} ->
note.("https://host.test/objects/1", "canonical")
# uploaded file claiming to be another object on the same host
%{method: :get, url: "https://host.test/media/evil.json"} ->
note.("https://host.test/objects/2", "spoofed")
%{method: :get, url: "https://host.test/objects/2"} ->
note.("https://host.test/objects/2", "real")
# canonical id does not serve itself
%{method: :get, url: "https://host.test/media/loop.json"} ->
note.("https://host.test/objects/3", "loop")
%{method: :get, url: "https://host.test/objects/3"} ->
note.("https://host.test/objects/4", "other")
# canonical id redirects
%{method: :get, url: "https://host.test/media/redirect.json"} ->
note.("https://host.test/objects/5", "redirect")
%{method: :get, url: "https://host.test/objects/5"} ->
%{note.("https://host.test/objects/5", "moved") | url: "https://host.test/media/x"}
%{method: :get, url: "https://host.test/objects/slash"} ->
note.("https://host.test/objects/slash/", "slash")
%{method: :get, url: "https://host.test/objects/no-id"} ->
note.(nil, "no id")
end)
:ok
end
test "it refetches display URLs from the canonical id" do
assert {:ok, %{"id" => "https://host.test/objects/1", "content" => "canonical"}} =
Fetcher.fetch_and_contain_remote_object_from_id("https://host.test/@actor/1")
end
test "it does not trust a document claiming another id on the same host" do
assert {:ok, %{"id" => "https://host.test/objects/2", "content" => "real"}} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://host.test/media/evil.json"
)
end
test "it refetches at most once" do
assert {:error, :id_mismatch} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://host.test/media/loop.json"
)
end
test "it does not follow redirects when refetching from the canonical id" do
assert {:error, _} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://host.test/media/redirect.json"
)
end
test "it ignores a trailing slash" do
assert {:ok, %{"content" => "slash"}} =
Fetcher.fetch_and_contain_remote_object_from_id("https://host.test/objects/slash")
end
test "it accepts ids that only differ by URL encoding" do
clear_config(:test_url_encoding, true)
mock(fn %{method: :get, url: url} ->
# the encoder sends uppercase escapes
assert url in [
"https://host.test/users/%E3%81%82",
"https://host.test/notes/%E3%81%82"
]
id =
if url =~ "users",
do: "https://host.test/users/あ",
else: "https://host.test/notes/%e3%81%82"
%Tesla.Env{
status: 200,
url: url,
headers: [{"content-type", "application/activity+json"}],
body: Jason.encode!(%{"id" => id, "type" => "Note"})
}
end)
assert {:ok, _} =
Fetcher.fetch_and_contain_remote_object_from_id("https://host.test/users/あ")
assert {:ok, _} =
Fetcher.fetch_and_contain_remote_object_from_id(
"https://host.test/notes/%e3%81%82"
)
end
test "it rejects documents without an id" do
assert {:error, _} =
Fetcher.fetch_and_contain_remote_object_from_id("https://host.test/objects/no-id")
end
end
describe "fetch with history" do
setup do
object2 = %{

6
test/pleroma/web/activity_pub/activity_pub_test.exs
View file

@ -541,7 +541,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubTest do
end
test "fetches user birthday information from misskey" do
user_id = "https://misskey.io/@mkljczk"
user_id = "https://misskey.io/users/8dhi2ne167"
Tesla.Mock.mock(fn
%{
@ -2058,7 +2058,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubTest do
json(
%{
"@context" => "https://www.w3.org/ns/activitystreams",
"id" => "https://remote.org/users/masto_hidden_counters/followers"
"id" => "https://remote.org/users/masto_hidden_counters/following"
},
headers: HttpRequestMock.activitypub_object_headers()
)
@ -2070,7 +2070,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubTest do
json(
%{
"@context" => "https://www.w3.org/ns/activitystreams",
"id" => "https://remote.org/users/masto_hidden_counters/following"
"id" => "https://remote.org/users/masto_hidden_counters/followers"
},
headers: HttpRequestMock.activitypub_object_headers()
)