🔒️(backend) verify participant presence before mute operations

Ensure the participant requesting a mute action is still present
in the room before processing the request.

This mitigates scenarios where a previously issued token could be
reused after the meeting has ended.

Current token lifetime is intentionally long-lived and will be
refactored in the future to better align with LiveKit session
constraints. In the meantime, add this extra validation step to
reduce the attack surface.

src/backend/core/api/viewsets.py

@@ -668,6 +668,26 @@ class RoomViewSet(
         serializer = serializers.MuteParticipantSerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
 
+        # TEMPORARY: a LiveKit token proves access was granted, not that the caller
+        # joined. Cross-check identity against the live participant list until auth
+        # is hardened. Skipped for non-LiveKit auth backends.
+        caller_identity = request.auth.identity if request.auth is not None else None
+        if caller_identity is not None:
+            try:
+                ParticipantsManagement().check_if_in_meeting(
+                    room_name=str(room.pk),
+                    identity=caller_identity,
+                )
+            except (ParticipantNotFoundException, ParticipantsManagementException):
+                logger.warning(
+                    "Failed to verify caller presence for mute in room %s; denying",
+                    room.pk,
+                )
+                return drf_response.Response(
+                    {"error": "Could not verify caller presence"},
+                    status=drf_status.HTTP_403_FORBIDDEN,
+                )
+
         try:
             ParticipantsManagement().mute(
                 room_name=str(room.pk),

src/backend/core/services/participants_management.py

@@ -15,6 +15,7 @@ from livekit.api import (
     TwirpError,
     UpdateParticipantRequest,
 )
+from livekit.protocol.models import ParticipantInfo
 
 from core import utils
 
@@ -154,3 +155,44 @@ class ParticipantsManagement:
 
         finally:
             await lkapi.aclose()
+
+    @async_to_sync
+    async def check_if_in_meeting(self, room_name: str, identity: str) -> bool:
+        """Check whether `identity` is currently a participant in `room_name`.
+
+        Raises ParticipantsManagementException for unexpected LiveKit errors
+        so callers can fail closed rather than silently allowing the action.
+        """
+
+        if not room_name or not identity:
+            return False
+
+        lkapi = utils.create_livekit_client()
+
+        try:
+            participant = await lkapi.room.get_participant(
+                RoomParticipantIdentity(
+                    room=room_name,
+                    identity=identity,
+                )
+            )
+        except TwirpError as e:
+            if e.code == "not_found":
+                raise ParticipantNotFoundException("Participant does not exist") from e
+
+            logger.exception(
+                "Unexpected error checking participant %s in room %s",
+                identity,
+                room_name,
+            )
+            raise ParticipantsManagementException(
+                "Could not verify participant presence"
+            ) from e
+
+        finally:
+            await lkapi.aclose()
+
+        return (
+            participant is not None
+            and participant.state != ParticipantInfo.State.DISCONNECTED
+        )

src/backend/core/tests/rooms/test_api_rooms_participants_management.py

@@ -2,7 +2,7 @@
 Test rooms API endpoints in the Meet core app: participants management.
 """
 
-# pylint: disable=redefined-outer-name,unused-argument,protected-access,no-name-in-module
+# pylint: disable=redefined-outer-name,unused-argument,protected-access,no-name-in-module,too-many-lines
 
 import random
 from unittest import mock
@@ -14,6 +14,7 @@ from django.urls import reverse
 
 import pytest
 from livekit.api import TwirpError, UpdateParticipantRequest
+from livekit.protocol.models import ParticipantInfo
 from rest_framework import status
 from rest_framework.test import APIClient
 
@@ -367,6 +368,141 @@ def test_mute_participant_admin_token_replayed_does_not_grant_admin(
     mock_livekit_client.room.mute_published_track.assert_not_called()
 
 
+def test_mute_participant_livekit_token_triggers_presence_check(mock_livekit_client):
+    """Should check participant presence when authenticated via LiveKit token only."""
+    client = APIClient()
+    room = RoomFactory()
+
+    user = AnonymousUser()
+    token = utils.generate_token(str(room.id), user, is_admin_or_owner=False)
+
+    url = reverse("rooms-mute-participant", kwargs={"pk": room.id})
+    response = client.post(
+        url,
+        {"participant_identity": str(uuid4()), "track_sid": "test-track-sid"},
+        format="json",
+        HTTP_AUTHORIZATION=f"Bearer {token}",
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    # Presence is verified against LiveKit before the mute is issued.
+    mock_livekit_client.room.get_participant.assert_called_once()
+    mock_livekit_client.room.mute_published_track.assert_called_once()
+
+
+def test_mute_participant_livekit_token_presence_check_returns_participant(
+    mock_livekit_client,
+):
+    """Should mute when the authentified participant is currently in the room."""
+    client = APIClient()
+    room = RoomFactory()
+
+    # Simulate LiveKit confirming the caller is currently in the room.
+    # State != DISCONNECTED (3) means present.
+    mock_livekit_client.room.get_participant.return_value = ParticipantInfo(
+        identity="caller-identity",
+        state=ParticipantInfo.State.ACTIVE,
+    )
+
+    user = AnonymousUser()
+    token = utils.generate_token(str(room.id), user, is_admin_or_owner=False)
+
+    url = reverse("rooms-mute-participant", kwargs={"pk": room.id})
+    response = client.post(
+        url,
+        {"participant_identity": str(uuid4()), "track_sid": "test-track-sid"},
+        format="json",
+        HTTP_AUTHORIZATION=f"Bearer {token}",
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    assert response.data == {"status": "success"}
+    mock_livekit_client.room.get_participant.assert_called_once()
+    mock_livekit_client.room.mute_published_track.assert_called_once()
+
+
+def test_mute_participant_livekit_token_presence_check_participant_not_found(
+    mock_livekit_client,
+):
+    """Should not mute when the authentified participant is not found."""
+    client = APIClient()
+    room = RoomFactory()
+
+    mock_livekit_client.room.get_participant.side_effect = TwirpError(
+        msg="participant does not exist", code="not_found", status=404
+    )
+
+    user = AnonymousUser()
+    token = utils.generate_token(str(room.id), user, is_admin_or_owner=False)
+
+    url = reverse("rooms-mute-participant", kwargs={"pk": room.id})
+    response = client.post(
+        url,
+        {"participant_identity": str(uuid4()), "track_sid": "test-track-sid"},
+        format="json",
+        HTTP_AUTHORIZATION=f"Bearer {token}",
+    )
+
+    assert response.status_code == status.HTTP_403_FORBIDDEN
+    assert response.data == {"error": "Could not verify caller presence"}
+    mock_livekit_client.room.get_participant.assert_called_once()
+    # The presence check failed, so we never reach the mute call.
+    mock_livekit_client.room.mute_published_track.assert_not_called()
+
+
+def test_mute_participant_livekit_token_presence_check_twirp_error_forbidden(
+    mock_livekit_client,
+):
+    """Should not mute when the presence check fail."""
+    client = APIClient()
+    room = RoomFactory()
+
+    mock_livekit_client.room.get_participant.side_effect = TwirpError(
+        msg="an error occured", code="not_found", status=500
+    )
+
+    user = AnonymousUser()
+    token = utils.generate_token(str(room.id), user, is_admin_or_owner=False)
+
+    url = reverse("rooms-mute-participant", kwargs={"pk": room.id})
+    response = client.post(
+        url,
+        {"participant_identity": str(uuid4()), "track_sid": "test-track-sid"},
+        format="json",
+        HTTP_AUTHORIZATION=f"Bearer {token}",
+    )
+
+    assert response.status_code == status.HTTP_403_FORBIDDEN
+    assert response.data == {"error": "Could not verify caller presence"}
+    mock_livekit_client.room.get_participant.assert_called_once()
+    # The presence check failed, so we never reach the mute call.
+    mock_livekit_client.room.mute_published_track.assert_not_called()
+
+
+def test_mute_participant_session_auth_skips_presence_check(mock_livekit_client):
+    """Should not check presence of the participant when authentified with a session cookie."""
+    client = APIClient()
+    room = RoomFactory()
+    user = UserFactory()
+    UserResourceAccessFactory(
+        resource=room, user=user, role=random.choice(["administrator", "owner"])
+    )
+    client.force_authenticate(user=user)
+
+    url = reverse("rooms-mute-participant", kwargs={"pk": room.id})
+    response = client.post(
+        url,
+        {"participant_identity": str(uuid4()), "track_sid": "test-track-sid"},
+        format="json",
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    # Session auth has no LiveKit identity to verify against, so the
+    # stop-gap presence check is skipped.
+    mock_livekit_client.room.get_participant.assert_not_called()
+    mock_livekit_client.room.mute_published_track.assert_called_once()
+
+
 def test_update_participant_success(mock_livekit_client):
     """Test successful participant update."""
     client = APIClient()