fix: treat empty MCP roots as explicit deny-all

README.md

@@ -157,8 +157,9 @@ Supported file-path tools:
 - `send_file`, `download_media`, `set_profile_photo`, `edit_chat_photo`, `send_voice`, `send_sticker`, `upload_file`
 
 Security semantics (aligned with MCP filesystem server):
-- Server-side allowlist via CLI positional arguments (fallback).
+- Server-side allowlist via CLI positional arguments (fallback when Roots API is unsupported).
 - Client-provided MCP Roots replace the server allowlist when available.
+- If the client returns an empty Roots list, file-path tools are disabled (deny-all).
 - All paths are resolved via realpath and must stay inside an allowed root.
 - Traversal/glob-like patterns are rejected (`..`, `*`, `?`, `~`, etc.).
 - Relative paths resolve against the first allowed root.

main.py

@@ -498,8 +498,8 @@ async def _get_effective_allowed_roots(ctx: Optional[Context]) -> List[Path]:
     if client_roots:
         return _dedupe_paths(client_roots)
 
-    # If client returned an empty roots list, keep server-side fallback roots.
+    # Roots API succeeded; an empty roots list is treated as explicit deny-all.
-    return fallback_roots
+    return []
 
 
 async def _ensure_allowed_roots(

test_file_path_security.py

@@ -122,25 +122,24 @@ async def test_client_roots_replace_server_allowlist(tmp_path, monkeypatch):
 
 
 @pytest.mark.asyncio
-async def test_empty_client_roots_fall_back_to_server_allowlist(tmp_path, monkeypatch):
+async def test_empty_client_roots_disable_file_tools(tmp_path, monkeypatch):
     server_root = (tmp_path / "server_root").resolve()
     server_root.mkdir(parents=True)
-    server_file = server_root / "server.txt"
-    server_file.write_text("server", encoding="utf-8")
 
     monkeypatch.setattr(main, "SERVER_ALLOWED_ROOTS", [server_root])
     ctx = _DummyContext([])
 
     roots = await main._get_effective_allowed_roots(ctx)
-    assert roots == [server_root]
+    assert roots == []
 
     resolved, error = await main._resolve_readable_file_path(
         raw_path="server.txt",
         ctx=ctx,
         tool_name="send_file",
     )
-    assert error is None
+    assert resolved is None
-    assert resolved == server_file.resolve()
+    assert error is not None
+    assert "disabled" in error
 
 
 @pytest.mark.asyncio