diff --git a/src/google/adk/cli/adk_web_server.py b/src/google/adk/cli/adk_web_server.py
index afedb7387a..6b775ed38f 100644
--- a/src/google/adk/cli/adk_web_server.py
+++ b/src/google/adk/cli/adk_web_server.py
@@ -692,6 +692,7 @@ def get_fast_api_app(
       register_processors: Callable[[TracerProvider], None] = lambda o: None,
       otel_to_cloud: bool = False,
       with_ui: bool = False,
+      ws_allowed_origins: Optional[set[str]] = None,
   ):
     """Creates a FastAPI app for the ADK web server.
 
@@ -1802,6 +1803,13 @@ async def run_agent_live(
         enable_affective_dialog: bool | None = Query(default=None),
         enable_session_resumption: bool | None = Query(default=None),
     ) -> None:
+      # Validate Origin header to prevent cross-origin WebSocket hijacking.
+      if ws_allowed_origins is not None:
+        origin = websocket.headers.get("origin")
+        if origin and origin not in ws_allowed_origins:
+          await websocket.close(code=1008, reason="Origin not allowed")
+          return
+
       await websocket.accept()
 
       session = await self.session_service.get_session(
diff --git a/src/google/adk/cli/fast_api.py b/src/google/adk/cli/fast_api.py
index 8f78c15f9b..8a4f3d2e4d 100644
--- a/src/google/adk/cli/fast_api.py
+++ b/src/google/adk/cli/fast_api.py
@@ -259,10 +259,26 @@ def tear_down_observer(observer: Observer, _: AdkWebServer):
         web_assets_dir=ANGULAR_DIST_PATH,
     )
 
+  # Build allowed origins for WebSocket CSRF protection.
+  ws_allowed_origins: Optional[set[str]] = {f"http://{host}:{port}"}
+  if host in ("0.0.0.0", "127.0.0.1", "localhost", "::1", "::"):
+    ws_allowed_origins.update({
+        f"http://localhost:{port}",
+        f"http://127.0.0.1:{port}",
+    })
+  if allow_origins:
+    for origin in allow_origins:
+      if origin == "*":
+        ws_allowed_origins = None
+        break
+      if not origin.startswith("regex:"):
+        ws_allowed_origins.add(origin)
+
   app = adk_web_server.get_fast_api_app(
       lifespan=lifespan,
       allow_origins=allow_origins,
       otel_to_cloud=otel_to_cloud,
+      ws_allowed_origins=ws_allowed_origins,
       **extra_fast_api_args,
   )
 
diff --git a/tests/unittests/cli/test_fast_api.py b/tests/unittests/cli/test_fast_api.py
index 0ea28e6683..070f1f445e 100755
--- a/tests/unittests/cli/test_fast_api.py
+++ b/tests/unittests/cli/test_fast_api.py
@@ -25,6 +25,7 @@
 from unittest.mock import patch
 
 from fastapi.testclient import TestClient
+from starlette.websockets import WebSocketDisconnect
 from google.adk.agents.base_agent import BaseAgent
 from google.adk.agents.run_config import RunConfig
 from google.adk.apps.app import App
@@ -1658,6 +1659,54 @@ def test_builder_save_rejects_traversal(builder_test_client, tmp_path):
   assert not (tmp_path / "app" / "tmp" / "escape.yaml").exists()
 
 
+@pytest.fixture
+def csrf_test_client(
+    mock_session_service,
+    mock_artifact_service,
+    mock_memory_service,
+    mock_agent_loader,
+    mock_eval_sets_manager,
+    mock_eval_set_results_manager,
+):
+  """TestClient with WebSocket origin checking enabled (no allow_origins='*')."""
+  return _create_test_client(
+      mock_session_service,
+      mock_artifact_service,
+      mock_memory_service,
+      mock_agent_loader,
+      mock_eval_sets_manager,
+      mock_eval_set_results_manager,
+      allow_origins=None,
+  )
+
+
+def test_ws_rejects_cross_origin(csrf_test_client, create_test_session):
+  """WebSocket connections with a foreign Origin must be rejected."""
+  info = create_test_session
+  with pytest.raises(WebSocketDisconnect) as exc_info:
+    with csrf_test_client.websocket_connect(
+        f"/run_live?app_name={info['app_name']}&user_id={info['user_id']}&session_id={info['session_id']}",
+        headers={"Origin": "http://evil.com"},
+    ):
+      pass
+  assert exc_info.value.code == 1008
+
+
+def test_ws_allows_same_origin(csrf_test_client, create_test_session):
+  """WebSocket connections from the server's own origin must not be rejected."""
+  info = create_test_session
+  try:
+    with csrf_test_client.websocket_connect(
+        f"/run_live?app_name={info['app_name']}&user_id={info['user_id']}&session_id={info['session_id']}",
+        headers={"Origin": "http://127.0.0.1:8000"},
+    ):
+      pass
+  except WebSocketDisconnect as e:
+    # Must not be rejected with 1008 (origin check).
+    # Other close codes (e.g. 1011 from dummy runner) are fine.
+    assert e.code != 1008
+
+
 def test_agent_run_resume_without_message_success(
     test_app, create_test_session
 ):