diff --git a/tests/conftest.py b/tests/conftest.py
index 8d5f191..c8a76fb 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -110,6 +110,23 @@ def guarded_getaddrinfo(host, *args, **kwargs):
     monkeypatch.setattr(socket.socket, "connect", guarded_connect)
     monkeypatch.setattr(socket.socket, "connect_ex", guarded_connect_ex)
     monkeypatch.setattr(socket, "getaddrinfo", guarded_getaddrinfo)
+
+    # yfinance sends through curl_cffi, whose libcurl opens sockets in C and never
+    # reaches the patches above.
+    try:
+        from curl_cffi import requests as curl_requests
+    except ImportError:
+        curl_requests = None
+    if curl_requests is not None:
+
+        def guarded_curl_request(session, method, url, *args, **kwargs):
+            reject_external(url)
+
+        async def guarded_async_curl_request(session, method, url, *args, **kwargs):
+            reject_external(url)
+
+        monkeypatch.setattr(curl_requests.Session, "request", guarded_curl_request)
+        monkeypatch.setattr(curl_requests.AsyncSession, "request", guarded_async_curl_request)
     yield
     if violations and not request.node.get_closest_marker("network_guard_probe"):
         pytest.fail(f"Offline test attempted external network access: {violations!r}")
diff --git a/tests/test_offline_network_policy.py b/tests/test_offline_network_policy.py
index 5374007..0d108b8 100644
--- a/tests/test_offline_network_policy.py
+++ b/tests/test_offline_network_policy.py
@@ -1,5 +1,6 @@
 """Offline test-lane network policy tests."""
 
+import asyncio
 import socket
 
 import pytest
@@ -28,3 +29,25 @@ def test_default_lane_allows_loopback_connections() -> None:
         with socket.create_connection(server.getsockname(), timeout=1):
             connection, _ = server.accept()
             connection.close()
+
+
+@pytest.mark.network_guard_probe
+def test_default_lane_rejects_curl_cffi_requests() -> None:
+    """yfinance's transport is libcurl, which never touches Python's socket module."""
+    curl_requests = pytest.importorskip("curl_cffi.requests")
+
+    with curl_requests.Session() as session:
+        with pytest.raises(RuntimeError, match="Offline test attempted"):
+            session.get("https://query1.finance.yahoo.com/v8/finance/chart/AAPL")
+
+
+@pytest.mark.network_guard_probe
+def test_default_lane_rejects_async_curl_cffi_requests() -> None:
+    curl_requests = pytest.importorskip("curl_cffi.requests")
+
+    async def fetch() -> None:
+        async with curl_requests.AsyncSession() as session:
+            await session.get("https://query1.finance.yahoo.com/v8/finance/chart/AAPL")
+
+    with pytest.raises(RuntimeError, match="Offline test attempted"):
+        asyncio.run(fetch())
diff --git a/tests/test_yahoo_provider.py b/tests/test_yahoo_provider.py
index ed77aac..2e43d3f 100644
--- a/tests/test_yahoo_provider.py
+++ b/tests/test_yahoo_provider.py
@@ -105,20 +105,19 @@ def test_fetch_minute_data(self, mock_download: MagicMock) -> None:
     @patch("ml4t.data.providers.yahoo.yf.download")
     def test_empty_response_handling(self, mock_download: MagicMock) -> None:
         """Test handling of empty responses."""
-        # Mock empty response
+        # Mock empty response, and an empty retry through Ticker.history
         mock_download.return_value = pd.DataFrame()
 
         provider = YahooFinanceProvider()
 
-        # Empty response should raise SymbolNotFoundError
-        from ml4t.data.core.exceptions import SymbolNotFoundError
-
-        with pytest.raises(SymbolNotFoundError):
-            provider.fetch_ohlcv(
-                symbol="INVALID",
-                start="2024-01-01",
-                end="2024-01-03",
-            )
+        with patch("ml4t.data.providers.yahoo.yf.Ticker") as mock_ticker:
+            mock_ticker.return_value.history.return_value = pd.DataFrame()
+            with pytest.raises(SymbolNotFoundError):
+                provider.fetch_ohlcv(
+                    symbol="INVALID",
+                    start="2024-01-01",
+                    end="2024-01-03",
+                )
 
     @patch("ml4t.data.providers.yahoo.yf.download")
     def test_rate_limiting(self, mock_download: MagicMock) -> None:
diff --git a/tests/test_yahoo_provider_edge_cases.py b/tests/test_yahoo_provider_edge_cases.py
index 8b9c784..1c698c9 100644
--- a/tests/test_yahoo_provider_edge_cases.py
+++ b/tests/test_yahoo_provider_edge_cases.py
@@ -27,8 +27,12 @@ def provider(self):
 
     def test_empty_data_raises_symbol_not_found(self, provider):
         """Test empty download raises SymbolNotFoundError."""
-        with patch("yfinance.download") as mock_download:
+        with (
+            patch("yfinance.download") as mock_download,
+            patch("ml4t.data.providers.yahoo.yf.Ticker") as mock_ticker,
+        ):
             mock_download.return_value = pd.DataFrame()
+            mock_ticker.return_value.history.return_value = pd.DataFrame()
 
             with pytest.raises(SymbolNotFoundError) as exc_info:
                 provider._fetch_and_transform_data(
@@ -74,8 +78,12 @@ def test_unknown_frequency_uses_daily_default(self, provider):
 
     def test_propagates_symbol_not_found_error(self, provider):
         """Test SymbolNotFoundError is propagated without wrapping."""
-        with patch("yfinance.download") as mock_download:
+        with (
+            patch("yfinance.download") as mock_download,
+            patch("ml4t.data.providers.yahoo.yf.Ticker") as mock_ticker,
+        ):
             mock_download.return_value = pd.DataFrame()  # Empty = not found
+            mock_ticker.return_value.history.return_value = pd.DataFrame()
 
             with pytest.raises(SymbolNotFoundError):
                 provider._fetch_and_transform_data("MISSING", "2024-01-01", "2024-01-31", "daily")