diff --git a/litellm/proxy/rag_endpoints/endpoints.py b/litellm/proxy/rag_endpoints/endpoints.py
index 3a50b703bc4..ecb13638648 100644
--- a/litellm/proxy/rag_endpoints/endpoints.py
+++ b/litellm/proxy/rag_endpoints/endpoints.py
@@ -15,6 +15,7 @@ from fastapi.responses import ORJSONResponse
 
 import litellm
 from litellm._logging import verbose_proxy_logger
+from litellm.constants import DEFAULT_MAX_RECURSE_DEPTH
 from litellm.proxy._types import *
 from litellm.proxy.auth.user_api_key_auth import UserAPIKeyAuth, user_api_key_auth
 from litellm.proxy.common_utils.http_parsing_utils import (
@@ -31,10 +32,17 @@ router = APIRouter()
 
 def _collect_vector_store_ids_from_payload(payload: Any) -> set[str]:
     vector_store_ids: set[str] = set()
-    payload_stack = [payload]
+    payload_stack = [(payload, 0)]
 
     while payload_stack:
-        current_payload = payload_stack.pop()
+        current_payload, depth = payload_stack.pop()
+        if depth > DEFAULT_MAX_RECURSE_DEPTH:
+            raise HTTPException(
+                status_code=400,
+                detail={
+                    "error": f"Max depth of {DEFAULT_MAX_RECURSE_DEPTH} exceeded while scanning vector_store_id values"
+                },
+            )
 
         if isinstance(current_payload, dict):
             for key, value in current_payload.items():
@@ -49,9 +57,9 @@ def _collect_vector_store_ids_from_payload(payload: Any) -> set[str]:
                     vector_store_ids.add(value)
                     continue
                 if isinstance(value, (dict, list)):
-                    payload_stack.append(value)
+                    payload_stack.append((value, depth + 1))
         elif isinstance(current_payload, list):
-            payload_stack.extend(current_payload)
+            payload_stack.extend((item, depth + 1) for item in current_payload)
 
     return vector_store_ids
 
diff --git a/litellm/proxy/vector_store_endpoints/endpoints.py b/litellm/proxy/vector_store_endpoints/endpoints.py
index 05423d9843d..86e316e7f40 100644
--- a/litellm/proxy/vector_store_endpoints/endpoints.py
+++ b/litellm/proxy/vector_store_endpoints/endpoints.py
@@ -20,29 +20,6 @@ router = APIRouter()
 ########################################################
 
 
-async def _check_vector_store_access(
-    vector_store: LiteLLM_ManagedVectorStore,
-    user_api_key_dict: UserAPIKeyAuth,
-) -> bool:
-    """
-    Check if the user has access to the vector store.
-
-    Delegates to :func:`can_user_access_vector_store`, which honors:
-    - PROXY_ADMIN bypass
-    - legacy vector stores with no team_id
-    - key-level and team-level ``object_permission.vector_stores`` allowlists
-    - team_id match between key and store
-    """
-    try:
-        await assert_user_can_access_vector_store(
-            vector_store=vector_store,
-            user_api_key_dict=user_api_key_dict,
-        )
-        return True
-    except HTTPException:
-        return False
-
-
 async def _update_request_data_with_litellm_managed_vector_store_registry(
     data: Dict,
     vector_store_id: str,
diff --git a/litellm/proxy/vector_store_endpoints/utils.py b/litellm/proxy/vector_store_endpoints/utils.py
index c09810d06dc..657b520b271 100644
--- a/litellm/proxy/vector_store_endpoints/utils.py
+++ b/litellm/proxy/vector_store_endpoints/utils.py
@@ -158,11 +158,15 @@ async def get_litellm_managed_vector_store(
             if vector_store is not None:
                 return _normalize_litellm_params(vector_store)
         except Exception as e:
-            verbose_proxy_logger.debug(
+            verbose_proxy_logger.warning(
                 "Failed to resolve vector store id=%s from registry: %s",
                 vector_store_id,
                 e,
             )
+            raise HTTPException(
+                status_code=500,
+                detail="Unable to validate vector store access",
+            ) from e
 
     try:
         from litellm.proxy.auth.auth_checks import (
@@ -188,12 +192,15 @@ async def get_litellm_managed_vector_store(
             LiteLLM_ManagedVectorStore(**rows[0].model_dump())
         )
     except Exception as e:
-        verbose_proxy_logger.debug(
+        verbose_proxy_logger.warning(
             "Failed to resolve vector store id=%s from shared cache: %s",
             vector_store_id,
             e,
         )
-        return None
+        raise HTTPException(
+            status_code=500,
+            detail="Unable to validate vector store access",
+        ) from e
 
 
 async def assert_user_can_access_vector_store(
diff --git a/litellm/proxy/vector_store_files_endpoints/endpoints.py b/litellm/proxy/vector_store_files_endpoints/endpoints.py
index ae8dc602e82..346a847c5dd 100644
--- a/litellm/proxy/vector_store_files_endpoints/endpoints.py
+++ b/litellm/proxy/vector_store_files_endpoints/endpoints.py
@@ -21,6 +21,7 @@ from litellm.proxy.vector_store_endpoints.utils import (
     is_allowed_to_call_vector_store_files_endpoint,
 )
 from litellm.types.utils import LlmProviders
+from litellm.types.vector_stores import LiteLLM_ManagedVectorStore
 
 if TYPE_CHECKING:
     from litellm.router import Router
@@ -194,6 +195,8 @@ def _update_request_data_with_litellm_managed_vector_store_registry(
     data: Dict,
     vector_store_id: str,
     llm_router: Optional["Router"] = None,
+    managed_vector_store: Optional[LiteLLM_ManagedVectorStore] = None,
+    should_lookup_registry: bool = True,
 ) -> Dict:
     """
     Update request data with model routing information from managed vector store.
@@ -263,23 +266,27 @@ def _update_request_data_with_litellm_managed_vector_store_registry(
 
         return data
 
-    # Legacy path: Check vector store registry for non-managed vector stores
-    if litellm.vector_store_registry is not None:
+    # Legacy path: Check vector store registry for non-managed vector stores.
+    vector_store_to_run = managed_vector_store
+    if (
+        vector_store_to_run is None
+        and should_lookup_registry
+        and litellm.vector_store_registry is not None
+    ):
         vector_store_to_run = litellm.vector_store_registry.get_litellm_managed_vector_store_from_registry(
             vector_store_id=vector_store_id
         )
-        if vector_store_to_run is not None:
-            if "custom_llm_provider" in vector_store_to_run:
-                data["custom_llm_provider"] = vector_store_to_run.get(
-                    "custom_llm_provider"
-                )
-            if "litellm_credential_name" in vector_store_to_run:
-                data["litellm_credential_name"] = vector_store_to_run.get(
-                    "litellm_credential_name"
-                )
-            if "litellm_params" in vector_store_to_run:
-                litellm_params = vector_store_to_run.get("litellm_params", {}) or {}
-                data.update(litellm_params)
+
+    if vector_store_to_run is not None:
+        if "custom_llm_provider" in vector_store_to_run:
+            data["custom_llm_provider"] = vector_store_to_run.get("custom_llm_provider")
+        if "litellm_credential_name" in vector_store_to_run:
+            data["litellm_credential_name"] = vector_store_to_run.get(
+                "litellm_credential_name"
+            )
+        if "litellm_params" in vector_store_to_run:
+            litellm_params = vector_store_to_run.get("litellm_params", {}) or {}
+            data.update(litellm_params)
 
     return data
 
@@ -365,7 +372,7 @@ async def vector_store_file_create(
 
     data = await _read_request_body(request=request)
     data["vector_store_id"] = vector_store_id
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
@@ -379,7 +386,11 @@ async def vector_store_file_create(
 
     # Then handle managed vector store IDs
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
@@ -464,13 +475,17 @@ async def vector_store_file_list(
     data: Dict[str, Optional[str]] = {"vector_store_id": vector_store_id}
     data.update(query_params)
     data["vector_store_id"] = vector_store_id
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
 
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
@@ -550,7 +565,7 @@ async def vector_store_file_retrieve(
         "vector_store_id": vector_store_id,
         "file_id": file_id,
     }
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
@@ -562,7 +577,11 @@ async def vector_store_file_retrieve(
 
     # Then handle managed vector store IDs
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
@@ -648,7 +667,7 @@ async def vector_store_file_content(
         "vector_store_id": vector_store_id,
         "file_id": file_id,
     }
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
@@ -660,7 +679,11 @@ async def vector_store_file_content(
 
     # Then handle managed vector store IDs
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
@@ -746,7 +769,7 @@ async def vector_store_file_update(
     data = await _read_request_body(request=request)
     data["vector_store_id"] = vector_store_id
     data["file_id"] = file_id
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
@@ -758,7 +781,11 @@ async def vector_store_file_update(
 
     # Then handle managed vector store IDs
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
@@ -844,7 +871,7 @@ async def vector_store_file_delete(
         "vector_store_id": vector_store_id,
         "file_id": file_id,
     }
-    await assert_user_can_access_vector_store_id(
+    managed_vector_store = await assert_user_can_access_vector_store_id(
         vector_store_id=vector_store_id,
         user_api_key_dict=user_api_key_dict,
     )
@@ -856,7 +883,11 @@ async def vector_store_file_delete(
 
     # Then handle managed vector store IDs
     data = _update_request_data_with_litellm_managed_vector_store_registry(
-        data=data, vector_store_id=vector_store_id, llm_router=llm_router
+        data=data,
+        vector_store_id=vector_store_id,
+        llm_router=llm_router,
+        managed_vector_store=managed_vector_store,
+        should_lookup_registry=False,
     )
 
     provider_enum = await _resolve_provider(data=data, request=request)
diff --git a/tests/test_litellm/proxy/vector_store_endpoints/test_vector_store_tenant_guard.py b/tests/test_litellm/proxy/vector_store_endpoints/test_vector_store_tenant_guard.py
index 2d6295e4029..380b3963c94 100644
--- a/tests/test_litellm/proxy/vector_store_endpoints/test_vector_store_tenant_guard.py
+++ b/tests/test_litellm/proxy/vector_store_endpoints/test_vector_store_tenant_guard.py
@@ -99,7 +99,8 @@ async def test_vector_store_file_create_forces_path_id_over_body_id():
 
     assert response == {"ok": True}
     assert captured_data["vector_store_id"] == "vs_path_allowed"
-    mock_registry.get_litellm_managed_vector_store_from_registry.assert_any_call(
+    assert captured_data["custom_llm_provider"] == "openai"
+    mock_registry.get_litellm_managed_vector_store_from_registry.assert_called_once_with(
         vector_store_id="vs_path_allowed"
     )
 
@@ -227,6 +228,25 @@ async def test_rag_ingest_denies_nested_other_team_vector_store():
     mock_aingest.assert_not_called()
 
 
+def test_rag_payload_scan_rejects_excessive_nesting():
+    from litellm.constants import DEFAULT_MAX_RECURSE_DEPTH
+    from litellm.proxy.rag_endpoints.endpoints import (
+        _collect_vector_store_ids_from_payload,
+    )
+
+    payload = {}
+    current = payload
+    for _ in range(DEFAULT_MAX_RECURSE_DEPTH + 1):
+        current["nested"] = {}
+        current = current["nested"]
+    current["vector_store_id"] = "vs_too_deep"
+
+    with pytest.raises(HTTPException) as exc_info:
+        _collect_vector_store_ids_from_payload(payload)
+
+    assert exc_info.value.status_code == 400
+
+
 @pytest.mark.asyncio
 async def test_responses_file_search_denies_other_team_vector_store():
     from litellm.proxy.common_request_processing import (
@@ -333,6 +353,24 @@ async def test_get_managed_vector_store_uses_shared_cache_helper_for_db_fallback
     cache_helper.assert_awaited_once()
 
 
+@pytest.mark.asyncio
+async def test_get_managed_vector_store_fails_closed_on_lookup_error():
+    from litellm.proxy.vector_store_endpoints.utils import (
+        get_litellm_managed_vector_store,
+    )
+
+    mock_registry = MagicMock()
+    mock_registry.get_litellm_managed_vector_store_from_registry.side_effect = (
+        RuntimeError("registry unavailable")
+    )
+
+    with patch.object(litellm, "vector_store_registry", mock_registry):
+        with pytest.raises(HTTPException) as exc_info:
+            await get_litellm_managed_vector_store(vector_store_id="vs_registry_only")
+
+    assert exc_info.value.status_code == 500
+
+
 @pytest.mark.asyncio
 async def test_vertex_discovery_allows_unregistered_provider_native_datastore_id():
     from litellm.proxy.pass_through_endpoints.llm_passthrough_endpoints import (