Merge branch 'master' into develop

8 files changed, 214 insertions, 7 deletions

diff --git a/CHANGES.md b/CHANGES.md
index 24f3d53a6d..7046c336a0 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,36 @@
 Users will stop receiving message updates via email for addresses that were previously linked to their account
 
+Synapse 1.41.1 (2021-08-31)
+===========================
+
+Due to the two security issues highlighted below, server administrators are encouraged to update Synapse. We are not aware of these vulnerabilities being exploited in the wild.
+
+Security advisory
+-----------------
+
+The following issues are fixed in v1.41.1.
+
+- **[GHSA-3x4c-pq33-4w3q](https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q) / [CVE-2021-39164](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-39164): Enumerating a private room's list of members and their display names.**
+
+  If an unauthorized user both knows the Room ID of a private room *and* that room's history visibility is set to `shared`, then they may be able to enumerate the room's members, including their display names.
+
+  The unauthorized user must be on the same homeserver as a user who is a member of the target room.
+
+  Fixed by [52c7a51cf](https://github.com/matrix-org/synapse/commit/52c7a51cf).
+
+- **[GHSA-jj53-8fmw-f2w2](https://github.com/matrix-org/synapse/security/advisories/GHSA-jj53-8fmw-f2w2) / [CVE-2021-39163](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-39163): Disclosing a private room's name, avatar, topic, and number of members.**
+
+  If an unauthorized user knows the Room ID of a private room, then its name, avatar, topic, and number of members may be disclosed through Group / Community features.
+
+  The unauthorized user must be on the same homeserver as a user who is a member of the target room, and their homeserver must allow non-administrators to create groups (`enable_group_creation` in the Synapse configuration; off by default).
+
+  Fixed by [cb35df940a](https://github.com/matrix-org/synapse/commit/cb35df940a), [\#10723](https://github.com/matrix-org/synapse/issues/10723).
+
+Bugfixes
+--------
+
+- Fix a regression introduced in Synapse 1.41 which broke email transmission on systems using older versions of the Twisted library. ([\#10713](https://github.com/matrix-org/synapse/issues/10713))
+
 Synapse 1.41.0 (2021-08-24)
 ===========================
 
diff --git a/changelog.d/10723.bugfix b/changelog.d/10723.bugfix
new file mode 100644
index 0000000000..e6ffdc9512
--- /dev/null
+++ b/changelog.d/10723.bugfix
@@ -0,0 +1 @@
+Fix unauthorised exposure of room metadata to communities.
diff --git a/debian/changelog b/debian/changelog
index 4da4bc018c..5f7a795b6e 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.41.1) stable; urgency=high
+
+  * New synapse release 1.41.1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 31 Aug 2021 12:59:10 +0100
+
 matrix-synapse-py3 (1.41.0) stable; urgency=medium
 
   * New synapse release 1.41.0.
diff --git a/synapse/__init__.py b/synapse/__init__.py
index ef3770262e..06d80f79b3 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -47,7 +47,7 @@ try:
 except ImportError:
     pass
 
-__version__ = "1.41.0"
+__version__ = "1.41.1"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when
diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
index 3dc55ab861..d6b75ac27f 100644
--- a/synapse/groups/groups_server.py
+++ b/synapse/groups/groups_server.py
@@ -332,6 +332,13 @@ class GroupsServerWorkerHandler:
             requester_user_id, group_id
         )
 
+        # Note! room_results["is_public"] is about whether the room is considered
+        # public from the group's point of view. (i.e. whether non-group members
+        # should be able to see the room is in the group).
+        # This is not the same as whether the room itself is public (in the sense
+        # of being visible in the room directory).
+        # As such, room_results["is_public"] itself is not sufficient to determine
+        # whether any given user is permitted to see the room's metadata.
         room_results = await self.store.get_rooms_in_group(
             group_id, include_private=is_user_in_group
         )
@@ -341,8 +348,15 @@ class GroupsServerWorkerHandler:
             room_id = room_result["room_id"]
 
             joined_users = await self.store.get_users_in_room(room_id)
+
+            # check the user is actually allowed to see the room before showing it to them
+            allow_private = requester_user_id in joined_users
+
             entry = await self.room_list_handler.generate_room_entry(
-                room_id, len(joined_users), with_alias=False, allow_private=True
+                room_id,
+                len(joined_users),
+                with_alias=False,
+                allow_private=allow_private,
             )
 
             if not entry:
@@ -354,7 +368,7 @@ class GroupsServerWorkerHandler:
 
         chunk.sort(key=lambda e: -e["num_joined_members"])
 
-        return {"chunk": chunk, "total_room_count_estimate": len(room_results)}
+        return {"chunk": chunk, "total_room_count_estimate": len(chunk)}
 
 
 class GroupsServerHandler(GroupsServerWorkerHandler):
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 8a0024ce84..101a29c6d3 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -183,20 +183,37 @@ class MessageHandler:
 
             if not last_events:
                 raise NotFoundError("Can't find event for token %s" % (at_token,))
+            last_event = last_events[0]
+
+            # check whether the user is in the room at that time to determine
+            # whether they should be treated as peeking.
+            state_map = await self.state_store.get_state_for_event(
+                last_event.event_id,
+                StateFilter.from_types([(EventTypes.Member, user_id)]),
+            )
+
+            joined = False
+            membership_event = state_map.get((EventTypes.Member, user_id))
+            if membership_event:
+                joined = membership_event.membership == Membership.JOIN
+
+            is_peeking = not joined
 
             visible_events = await filter_events_for_client(
                 self.storage,
                 user_id,
                 last_events,
                 filter_send_to_client=False,
+                is_peeking=is_peeking,
             )
 
-            event = last_events[0]
             if visible_events:
                 room_state_events = await self.state_store.get_state_for_events(
-                    [event.event_id], state_filter=state_filter
+                    [last_event.event_id], state_filter=state_filter
                 )
-                room_state: Mapping[Any, EventBase] = room_state_events[event.event_id]
+                room_state: Mapping[Any, EventBase] = room_state_events[
+                    last_event.event_id
+                ]
             else:
                 raise AuthError(
                     403,
diff --git a/tests/rest/client/test_groups.py b/tests/rest/client/test_groups.py
new file mode 100644
index 0000000000..ad0425ae65
--- /dev/null
+++ b/tests/rest/client/test_groups.py
@@ -0,0 +1,56 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.rest.client import groups, room
+
+from tests import unittest
+from tests.unittest import override_config
+
+
+class GroupsTestCase(unittest.HomeserverTestCase):
+    user_id = "@alice:test"
+    room_creator_user_id = "@bob:test"
+
+    servlets = [room.register_servlets, groups.register_servlets]
+
+    @override_config({"enable_group_creation": True})
+    def test_rooms_limited_by_visibility(self):
+        group_id = "+spqr:test"
+
+        # Alice creates a group
+        channel = self.make_request("POST", "/create_group", {"localpart": "spqr"})
+        self.assertEquals(channel.code, 200, msg=channel.text_body)
+        self.assertEquals(channel.json_body, {"group_id": group_id})
+
+        # Bob creates a private room
+        room_id = self.helper.create_room_as(self.room_creator_user_id, is_public=False)
+        self.helper.auth_user_id = self.room_creator_user_id
+        self.helper.send_state(
+            room_id, "m.room.name", {"name": "bob's secret room"}, tok=None
+        )
+        self.helper.auth_user_id = self.user_id
+
+        # Alice adds the room to her group.
+        channel = self.make_request(
+            "PUT", f"/groups/{group_id}/admin/rooms/{room_id}", {}
+        )
+        self.assertEquals(channel.code, 200, msg=channel.text_body)
+        self.assertEquals(channel.json_body, {})
+
+        # Alice now tries to retrieve the room list of the space.
+        channel = self.make_request("GET", f"/groups/{group_id}/rooms")
+        self.assertEquals(channel.code, 200, msg=channel.text_body)
+        self.assertEquals(
+            channel.json_body, {"chunk": [], "total_room_count_estimate": 0}
+        )
diff --git a/tests/rest/client/test_rooms.py b/tests/rest/client/test_rooms.py
index 0c9cbb9aff..50100a5ae4 100644
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@@ -29,7 +29,7 @@ from synapse.api.constants import EventContentFields, EventTypes, Membership
 from synapse.api.errors import HttpResponseException
 from synapse.handlers.pagination import PurgeStatus
 from synapse.rest import admin
-from synapse.rest.client import account, directory, login, profile, room
+from synapse.rest.client import account, directory, login, profile, room, sync
 from synapse.types import JsonDict, RoomAlias, UserID, create_requester
 from synapse.util.stringutils import random_string
 
@@ -381,6 +381,8 @@ class RoomPermissionsTestCase(RoomBase):
 class RoomsMemberListTestCase(RoomBase):
     """Tests /rooms/$room_id/members/list REST events."""
 
+    servlets = RoomBase.servlets + [sync.register_servlets]
+
     user_id = "@sid1:red"
 
     def test_get_member_list(self):
@@ -397,6 +399,86 @@ class RoomsMemberListTestCase(RoomBase):
         channel = self.make_request("GET", "/rooms/%s/members" % room_id)
         self.assertEquals(403, channel.code, msg=channel.result["body"])
 
+    def test_get_member_list_no_permission_with_at_token(self):
+        """
+        Tests that a stranger to the room cannot get the member list
+        (in the case that they use an at token).
+        """
+        room_id = self.helper.create_room_as("@someone.else:red")
+
+        # first sync to get an at token
+        channel = self.make_request("GET", "/sync")
+        self.assertEquals(200, channel.code)
+        sync_token = channel.json_body["next_batch"]
+
+        # check that permission is denied for @sid1:red to get the
+        # memberships of @someone.else:red's room.
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{room_id}/members?at={sync_token}",
+        )
+        self.assertEquals(403, channel.code, msg=channel.result["body"])
+
+    def test_get_member_list_no_permission_former_member(self):
+        """
+        Tests that a former member of the room can not get the member list.
+        """
+        # create a room, invite the user and the user joins
+        room_id = self.helper.create_room_as("@alice:red")
+        self.helper.invite(room_id, "@alice:red", self.user_id)
+        self.helper.join(room_id, self.user_id)
+
+        # check that the user can see the member list to start with
+        channel = self.make_request("GET", "/rooms/%s/members" % room_id)
+        self.assertEquals(200, channel.code, msg=channel.result["body"])
+
+        # ban the user
+        self.helper.change_membership(room_id, "@alice:red", self.user_id, "ban")
+
+        # check the user can no longer see the member list
+        channel = self.make_request("GET", "/rooms/%s/members" % room_id)
+        self.assertEquals(403, channel.code, msg=channel.result["body"])
+
+    def test_get_member_list_no_permission_former_member_with_at_token(self):
+        """
+        Tests that a former member of the room can not get the member list
+        (in the case that they use an at token).
+        """
+        # create a room, invite the user and the user joins
+        room_id = self.helper.create_room_as("@alice:red")
+        self.helper.invite(room_id, "@alice:red", self.user_id)
+        self.helper.join(room_id, self.user_id)
+
+        # sync to get an at token
+        channel = self.make_request("GET", "/sync")
+        self.assertEquals(200, channel.code)
+        sync_token = channel.json_body["next_batch"]
+
+        # check that the user can see the member list to start with
+        channel = self.make_request(
+            "GET", "/rooms/%s/members?at=%s" % (room_id, sync_token)
+        )
+        self.assertEquals(200, channel.code, msg=channel.result["body"])
+
+        # ban the user (Note: the user is actually allowed to see this event and
+        # state so that they know they're banned!)
+        self.helper.change_membership(room_id, "@alice:red", self.user_id, "ban")
+
+        # invite a third user and let them join
+        self.helper.invite(room_id, "@alice:red", "@bob:red")
+        self.helper.join(room_id, "@bob:red")
+
+        # now, with the original user, sync again to get a new at token
+        channel = self.make_request("GET", "/sync")
+        self.assertEquals(200, channel.code)
+        sync_token = channel.json_body["next_batch"]
+
+        # check the user can no longer see the updated member list
+        channel = self.make_request(
+            "GET", "/rooms/%s/members?at=%s" % (room_id, sync_token)
+        )
+        self.assertEquals(403, channel.code, msg=channel.result["body"])
+
     def test_get_member_list_mixed_memberships(self):
         room_creator = "@some_other_guy:red"
         room_id = self.helper.create_room_as(room_creator)