feat(core): Harden native Python task runner (no-changelog) (#18826)

packages/@n8n/task-runner-python/src/task_executor.py

@@ -3,6 +3,8 @@ import multiprocessing
 import traceback
 import textwrap
 import json
+import os
+import sys
 
 from src.errors import (
     TaskResultMissingError,
@@ -11,9 +13,9 @@ from src.errors import (
     TaskProcessExitError,
 )
 
-from .message_types.broker import NodeMode, Items
-from .constants import EXECUTOR_CIRCULAR_REFERENCE_KEY, EXECUTOR_USER_OUTPUT_KEY
-from typing import Any
+from src.message_types.broker import NodeMode, Items
+from src.constants import EXECUTOR_CIRCULAR_REFERENCE_KEY, EXECUTOR_USER_OUTPUT_KEY
+from typing import Any, Set
 
 from multiprocessing.context import SpawnProcess
 
@@ -26,7 +28,14 @@ class TaskExecutor:
     """Responsible for executing Python code tasks in isolated subprocesses."""
 
     @staticmethod
-    def create_process(code: str, node_mode: NodeMode, items: Items):
+    def create_process(
+        code: str,
+        node_mode: NodeMode,
+        items: Items,
+        stdlib_allow: Set[str],
+        external_allow: Set[str],
+        builtins_deny: set[str],
+    ):
         """Create a subprocess for executing a Python code task and a queue for communication."""
 
         fn = (
@@ -36,7 +45,10 @@ class TaskExecutor:
         )
 
         queue = MULTIPROCESSING_CONTEXT.Queue()
-        process = MULTIPROCESSING_CONTEXT.Process(target=fn, args=(code, items, queue))
+        process = MULTIPROCESSING_CONTEXT.Process(
+            target=fn,
+            args=(code, items, queue, stdlib_allow, external_allow, builtins_deny),
+        )
 
         return process, queue
 
@@ -95,16 +107,27 @@ class TaskExecutor:
             process.kill()
 
     @staticmethod
-    def _all_items(raw_code: str, items: Items, queue: multiprocessing.Queue):
+    def _all_items(
+        raw_code: str,
+        items: Items,
+        queue: multiprocessing.Queue,
+        stdlib_allow: Set[str],
+        external_allow: Set[str],
+        builtins_deny: set[str],
+    ):
         """Execute a Python code task in all-items mode."""
 
+        os.environ.clear()
+
+        TaskExecutor._sanitize_sys_modules(stdlib_allow, external_allow)
+
         print_args: PrintArgs = []
 
         try:
             code = TaskExecutor._wrap_code(raw_code)
 
             globals = {
-                "__builtins__": __builtins__,
+                "__builtins__": TaskExecutor._filter_builtins(builtins_deny),
                 "_items": items,
                 "print": TaskExecutor._create_custom_print(print_args),
             }
@@ -119,9 +142,20 @@ class TaskExecutor:
             TaskExecutor._put_error(queue, e, print_args)
 
     @staticmethod
-    def _per_item(raw_code: str, items: Items, queue: multiprocessing.Queue):
+    def _per_item(
+        raw_code: str,
+        items: Items,
+        queue: multiprocessing.Queue,
+        stdlib_allow: Set[str],
+        external_allow: Set[str],
+        builtins_deny: set[str],
+    ):
         """Execute a Python code task in per-item mode."""
 
+        os.environ.clear()
+
+        TaskExecutor._sanitize_sys_modules(stdlib_allow, external_allow)
+
         print_args: PrintArgs = []
 
         try:
@@ -131,7 +165,7 @@ class TaskExecutor:
             result = []
             for index, item in enumerate(items):
                 globals = {
-                    "__builtins__": __builtins__,
+                    "__builtins__": TaskExecutor._filter_builtins(builtins_deny),
                     "_item": item,
                     "print": TaskExecutor._create_custom_print(print_args),
                 }
@@ -195,7 +229,7 @@ class TaskExecutor:
     @staticmethod
     def _format_print_args(*args) -> list[str]:
         """
-        Takes the arguments passed to a `print()` call in user code and converts them
+        Takes the args passed to a `print()` call in user code and converts them
         to string representations suitable for display in a browser console.
 
         Expects all args to be serializable.
@@ -217,3 +251,45 @@ class TaskExecutor:
                 formatted.append(json.dumps(arg, default=str, ensure_ascii=False))
 
         return formatted
+
+    # ========== security ==========
+
+    @staticmethod
+    def _filter_builtins(builtins_deny: set[str]):
+        """Get __builtins__ with denied ones removed."""
+
+        if len(builtins_deny) == 0:
+            return __builtins__
+
+        return {k: v for k, v in __builtins__.items() if k not in builtins_deny}
+
+    @staticmethod
+    def _sanitize_sys_modules(stdlib_allow: Set[str], external_allow: Set[str]):
+        safe_modules = {
+            "builtins",
+            "__main__",
+            "sys",
+            "traceback",
+            "linecache",
+        }
+
+        if "*" in stdlib_allow:
+            safe_modules.update(sys.stdlib_module_names)
+        else:
+            safe_modules.update(stdlib_allow)
+
+        if "*" in external_allow:
+            safe_modules.update(
+                name
+                for name in sys.modules.keys()
+                if name not in sys.stdlib_module_names
+            )
+        else:
+            safe_modules.update(external_allow)
+
+        modules_to_remove = [
+            name for name in sys.modules.keys() if name not in safe_modules
+        ]
+
+        for module_name in modules_to_remove:
+            del sys.modules[module_name]