🔒️(backend) enhance API input validation to strengthen security

During the bug bounty, attempts were made to pass unexpected hidden
fields to manipulate room behavior and join as a ghost.

Treat these parameters as suspicious. They are not sent by the
frontend, so their presence likely indicates tampering.

Explicitly allow the parameters but emit warning logs to help detect
and investigate suspicious activity.

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

@@ -8,6 +8,7 @@ import random
 from unittest import mock
 from uuid import uuid4
 
+from django.core.exceptions import SuspiciousOperation
 from django.urls import reverse
 
 import pytest
@@ -132,11 +133,7 @@ def test_update_participant_success(mock_livekit_client):
                 1,
                 2,
             ],  # [TrackSource.CAMERA, TrackSource.MICROPHONE]
-            "hidden": False,
-            "recorder": False,
             "can_update_metadata": True,
-            "agent": False,
-            "can_subscribe_metrics": False,
         },
         "name": "John Doe",
     }
@@ -151,6 +148,151 @@ def test_update_participant_success(mock_livekit_client):
     mock_livekit_client.aclose.assert_called_once()
 
 
+@pytest.mark.parametrize(
+    "permission_payload",
+    [
+        {},  # empty dict is valid
+        {"can_subscribe": True},
+        {"can_publish": True},
+        {"can_publish_data": True},
+        {"can_publish_sources": [1, 2]},
+        {"can_update_metadata": True},
+    ],
+)
+def test_update_participant_permission_fields_are_optional(
+    mock_livekit_client, permission_payload
+):
+    """Test that each required permission field can be passed individually."""
+    client = APIClient()
+    room = RoomFactory()
+    user = UserFactory()
+    UserResourceAccessFactory(
+        resource=room, user=user, role=random.choice(["administrator", "owner"])
+    )
+    client.force_authenticate(user=user)
+
+    payload = {
+        "participant_identity": str(uuid4()),
+        "permission": permission_payload,
+    }
+
+    url = reverse("rooms-update-participant", kwargs={"pk": room.id})
+    response = client.post(url, payload, format="json")
+
+    assert response.status_code == status.HTTP_200_OK
+    assert response.data == {"status": "success"}
+
+    mock_livekit_client.room.update_participant.assert_called_once()
+    mock_livekit_client.aclose.assert_called_once()
+
+
+@pytest.mark.parametrize(
+    "value,permission_key",
+    [
+        (False, "hidden"),
+        (True, "hidden"),
+        (False, "recorder"),
+        (True, "recorder"),
+        (False, "agent"),
+        (True, "agent"),
+    ],
+)
+@mock.patch("core.api.serializers.SuspiciousOperation", side_effect=SuspiciousOperation)
+def test_update_participant_suspicious_permission(
+    mock_suspicious, value, permission_key
+):
+    """Test update participant raises 400 when a restricted permission is set."""
+    client = APIClient()
+    room = RoomFactory()
+    user = UserFactory()
+    UserResourceAccessFactory(
+        resource=room, user=user, role=random.choice(["administrator", "owner"])
+    )
+    client.force_authenticate(user=user)
+
+    payload = {
+        "participant_identity": str(uuid4()),
+        "permission": {
+            "can_subscribe": True,
+            "can_publish": True,
+            "can_publish_data": True,
+            "can_update_metadata": False,
+            permission_key: value,
+        },
+    }
+
+    url = reverse("rooms-update-participant", kwargs={"pk": room.id})
+    response = client.post(url, payload, format="json")
+
+    assert response.status_code == status.HTTP_400_BAD_REQUEST
+    mock_suspicious.assert_called_once_with(
+        f"Setting the following participant permissions is not allowed: {permission_key}."
+    )
+
+
+@mock.patch("core.api.serializers.SuspiciousOperation", side_effect=SuspiciousOperation)
+def test_update_participant_suspicious_permission_multiple(mock_suspicious):
+    """Test update participant raises 400 when multiple suspicious permissions are set."""
+    client = APIClient()
+    room = RoomFactory()
+    user = UserFactory()
+    UserResourceAccessFactory(
+        resource=room, user=user, role=random.choice(["administrator", "owner"])
+    )
+    client.force_authenticate(user=user)
+
+    payload = {
+        "participant_identity": str(uuid4()),
+        "permission": {
+            "can_subscribe": True,
+            "can_publish": True,
+            "can_publish_data": True,
+            "hidden": True,
+            "recorder": False,
+            "can_update_metadata": False,
+            "agent": True,
+            "can_subscribe_metrics": False,
+        },
+    }
+
+    url = reverse("rooms-update-participant", kwargs={"pk": room.id})
+    response = client.post(url, payload, format="json")
+
+    assert response.status_code == status.HTTP_400_BAD_REQUEST
+    mock_suspicious.assert_called_once_with(
+        "Setting the following participant permissions is not allowed: hidden, recorder, agent."
+    )
+
+
+@pytest.mark.parametrize("value", (False, True))
+def test_update_participant_unimplemented_can_subscribe_metrics(value):
+    """Test update participant raises 400 when can_subscribe_metrics is set."""
+    client = APIClient()
+    room = RoomFactory()
+    user = UserFactory()
+    UserResourceAccessFactory(
+        resource=room, user=user, role=random.choice(["administrator", "owner"])
+    )
+    client.force_authenticate(user=user)
+
+    payload = {
+        "participant_identity": str(uuid4()),
+        "permission": {
+            "can_subscribe": True,
+            "can_publish": True,
+            "can_publish_data": True,
+            "can_update_metadata": False,
+            "can_subscribe_metrics": value,
+        },
+    }
+
+    url = reverse("rooms-update-participant", kwargs={"pk": room.id})
+    response = client.post(url, payload, format="json")
+
+    assert response.status_code == status.HTTP_400_BAD_REQUEST
+    assert "can_subscribe_metrics" in str(response.data)
+
+
 def test_update_participant_forbidden_without_access():
     """Test update participant returns 403 when user lacks room privileges."""
     client = APIClient()
@@ -226,7 +368,17 @@ def test_update_participant_invalid_permission():
     response = client.post(url, payload, format="json")
 
     assert response.status_code == status.HTTP_400_BAD_REQUEST
-    assert "Invalid permission" in str(response.data)
+    assert response.json() == {
+        "permission": [
+            {
+                "type": "extra_forbidden",
+                "loc": ["invalid-attributes"],
+                "msg": "Extra inputs are not permitted",
+                "input": "True",
+                "url": "https://errors.pydantic.dev/2.12/v/extra_forbidden",
+            },
+        ]
+    }
 
 
 def test_update_participant_wrong_metadata_attributes():