fix(api): authorize deprecated vertex streams

Author: erichare

src/backend/base/langflow/api/v1/chat.py

@@ -46,7 +46,7 @@
     VerticesOrderResponse,
 )
 from langflow.exceptions.component import ComponentBuildError
-from langflow.services.auth.utils import get_current_active_user, get_current_user_optional
+from langflow.services.auth.utils import get_current_user_optional
 from langflow.services.authorization import FlowAction, ensure_flow_permission
 from langflow.services.authorization.fetch import deny_to_404
 from langflow.services.chat.service import ChatService
@@ -690,12 +690,12 @@ async def _stream_vertex(flow_id: str, vertex_id: str, chat_service: ChatService
     "/build/{flow_id}/{vertex_id}/stream",
     response_class=StreamingResponse,
     deprecated=True,
-    dependencies=[Depends(get_current_active_user)],
     include_in_schema=False,
 )
 async def build_vertex_stream(
     flow_id: uuid.UUID,
     vertex_id: str,
+    current_user: CurrentActiveUser,
 ):
     """Build a vertex instead of the entire graph.
 
@@ -722,6 +722,28 @@ async def build_vertex_stream(
     Raises:
         HTTPException: If an error occurs while building the vertex.
     """
+    # The cache is keyed only by flow UUID and may contain another user's
+    # in-memory graph. Authorize before constructing the streaming response so
+    # an authenticated non-owner cannot read a built result or invoke
+    # ``vertex.stream()`` on that cached graph.
+    async with session_scope() as session:
+        stmt = (
+            select(Flow)
+            .where(Flow.id == flow_id)
+            .where((Flow.user_id == current_user.id) | (Flow.access_type == AccessTypeEnum.PUBLIC))
+        )
+        flow = (await session.exec(stmt)).first()
+    if not flow:
+        raise HTTPException(status_code=404, detail=f"Flow with id {flow_id} not found")
+    await ensure_flow_permission(
+        current_user,
+        FlowAction.EXECUTE,
+        flow_id=flow_id,
+        flow_user_id=flow.user_id,
+        workspace_id=flow.workspace_id,
+        folder_id=flow.folder_id,
+    )
+
     try:
         return StreamingResponse(
             _stream_vertex(str(flow_id), vertex_id, get_chat_service()),

src/backend/tests/unit/test_endpoints.py

@@ -426,6 +426,18 @@ async def test_build_vertex_returns_404_for_other_users_private_flow(
     assert response.status_code == 404, response.text
 
 
+async def test_build_vertex_stream_returns_404_for_other_users_private_flow(
+    client, added_flow_webhook_test, second_user_headers
+):
+    """The deprecated stream route must authorize before reading the shared graph cache."""
+    flow_id = added_flow_webhook_test["id"]
+    response = await client.get(
+        f"/api/v1/build/{flow_id}/ChatInput-some-id/stream",
+        headers=second_user_headers,
+    )
+    assert response.status_code == 404, response.text
+
+
 async def test_build_vertex_invalid_vertex_id(client, added_flow_webhook_test, logged_in_headers):
     flow_id = added_flow_webhook_test["id"]
     response = await client.post(f"/api/v1/build/{flow_id}/vertices/invalid_vertex_id", headers=logged_in_headers)