security: restrict pickle deserialization in v0 schema and migration tool

src/google/adk/sessions/migration/migrate_from_sqlalchemy_pickle.py

@@ -29,6 +29,7 @@
 from google.adk.sessions import _session_util
 from google.adk.sessions.migration import _schema_check_utils
 from google.adk.sessions.schemas import v1
+from google.adk.sessions.schemas._safe_unpickle import safe_loads as _safe_pickle_loads
 from google.genai import types
 import sqlalchemy
 from sqlalchemy import create_engine
@@ -59,7 +60,7 @@ def _row_to_event(row: dict) -> Event:
   if actions_val is not None:
     try:
       if isinstance(actions_val, bytes):
-        actions = pickle.loads(actions_val)
+        actions = _safe_pickle_loads(actions_val)
       else:  # for spanner - it might return object directly
         actions = actions_val
     except Exception as e:

src/google/adk/sessions/schemas/_safe_unpickle.py

@@ -0,0 +1,101 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Restricted unpickler for safe deserialization of v0 EventActions data.
+
+The v0 schema stored EventActions as pickle blobs. This module provides a
+safe deserialization path that only allows known ADK and standard types,
+blocking arbitrary code execution via crafted pickle payloads.
+
+See: https://docs.python.org/3/library/pickle.html#restricting-globals
+"""
+
+from __future__ import annotations
+
+import io
+import logging
+import os
+import pickle
+from typing import Any
+
+logger = logging.getLogger("google_adk." + __name__)
+
+_ALLOWED_MODULE_PREFIXES: tuple[str, ...] = (
+    "google.adk.",
+    "google.genai.",
+    "pydantic.",
+    "pydantic_core.",
+)
+
+_ALLOWED_GLOBALS: dict[str, set[str]] = {
+    "builtins": {
+        "dict",
+        "list",
+        "set",
+        "tuple",
+        "frozenset",
+        "bytes",
+        "bytearray",
+        "True",
+        "False",
+        "None",
+        "type",
+        "object",
+        "complex",
+        "slice",
+        "range",
+        "int",
+        "float",
+        "str",
+        "bool",
+    },
+    "collections": {"OrderedDict", "defaultdict"},
+    "datetime": {"datetime", "date", "time", "timedelta", "timezone"},
+    "copy_reg": {"_reconstructor"},
+    "copyreg": {"_reconstructor", "__newobj__"},
+    "_codecs": {"encode"},
+    "enum": {"__new__", "Enum", "IntEnum", "StrEnum"},
+}
+
+
+class _RestrictedUnpickler(pickle.Unpickler):
+  """Unpickler that only allows reconstruction of known-safe types."""
+
+  def find_class(self, module: str, name: str) -> Any:
+    for prefix in _ALLOWED_MODULE_PREFIXES:
+      if module.startswith(prefix):
+        return super().find_class(module, name)
+    allowed_names = _ALLOWED_GLOBALS.get(module)
+    if allowed_names and name in allowed_names:
+      return super().find_class(module, name)
+    raise pickle.UnpicklingError(
+        f"Blocked unsafe pickle global: {module}.{name}. "
+        "If this is a legitimate ADK type, please file an issue at "
+        "https://github.com/google/adk-python/issues"
+    )
+
+
+def safe_loads(data: bytes) -> Any:
+  """Deserialize pickle bytes using a restricted unpickler.
+
+  If ADK_ALLOW_UNSAFE_V0_PICKLE=1 is set, falls back to unrestricted
+  pickle.loads() for compatibility. A deprecation warning is logged.
+  """
+  if os.environ.get("ADK_ALLOW_UNSAFE_V0_PICKLE") == "1":
+    logger.warning(
+        "ADK_ALLOW_UNSAFE_V0_PICKLE is set - using unrestricted "
+        "pickle.loads(). This is unsafe and will be removed in a "
+        "future release. Migrate to the v1 JSON schema."
+    )
+    return pickle.loads(data)  # noqa: S301
+  return _RestrictedUnpickler(io.BytesIO(data)).load()

src/google/adk/sessions/schemas/v0.py

@@ -57,6 +57,7 @@
 from ...events.event import Event
 from ...events.event_actions import EventActions
 from ..session import Session
+from ._safe_unpickle import safe_loads as _safe_pickle_loads
 from .shared import DEFAULT_MAX_KEY_LENGTH
 from .shared import DEFAULT_MAX_VARCHAR_LENGTH
 from .shared import DynamicJSON
@@ -110,11 +111,24 @@ def process_bind_param(self, value, dialect):
         return pickle.dumps(value)
     return value
 
+  def result_processor(self, dialect, coltype):
+    if dialect.name in ("mysql", "spanner+spanner"):
+      return super().result_processor(dialect, coltype)
+
+    def process(value):
+      if value is None:
+        return None
+      if isinstance(value, memoryview):
+        value = bytes(value)
+      return _safe_pickle_loads(value)
+
+    return process
+
   def process_result_value(self, value, dialect):
     """Ensures the raw bytes from the database are unpickled back into a Python object."""
     if value is not None:
       if dialect.name in ("spanner+spanner", "mysql"):
-        return pickle.loads(value)
+        return _safe_pickle_loads(value)
     return value
 
 

tests/unittests/sessions/test_safe_unpickle.py

@@ -0,0 +1,139 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for _safe_unpickle RestrictedUnpickler."""
+
+from __future__ import annotations
+
+import io
+import os
+import pickle
+import struct
+import unittest
+
+from google.adk.sessions.schemas._safe_unpickle import safe_loads
+
+
+def _make_global_payload(module: str, func: str, *args: str) -> bytes:
+    """Craft a pickle stream that calls module.func(*args)."""
+    buf = io.BytesIO()
+    buf.write(pickle.PROTO + struct.pack("B", 2))
+    buf.write(b"c" + f"{module}\n{func}\n".encode())
+    buf.write(b"(")
+    for arg in args:
+        encoded = arg.encode("utf-8")
+        buf.write(
+            pickle.SHORT_BINUNICODE + struct.pack("<B", len(encoded)) + encoded
+        )
+    buf.write(b"t")
+    buf.write(b"R")
+    buf.write(b".")
+    return buf.getvalue()
+
+
+class TestBlockedPayloads(unittest.TestCase):
+    """Malicious pickle payloads must be blocked."""
+
+    def test_os_system(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(_make_global_payload("os", "system", "echo pwned"))
+
+    def test_subprocess_popen(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(_make_global_payload("subprocess", "Popen", "id"))
+
+    def test_builtins_import(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(_make_global_payload("builtins", "__import__", "os"))
+
+    def test_posix_system(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(_make_global_payload("posix", "system", "whoami"))
+
+    def test_nt_system(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(_make_global_payload("nt", "system", "whoami"))
+
+    def test_builtins_eval(self):
+        with self.assertRaises(pickle.UnpicklingError):
+            safe_loads(
+                _make_global_payload(
+                    "builtins", "eval", "__import__('os').system('id')"
+                )
+            )
+
+
+class TestEventActionsRoundTrip(unittest.TestCase):
+    """Legitimate EventActions data must survive pickle -> safe_loads."""
+
+    def _round_trip(self, obj):
+        return safe_loads(pickle.dumps(obj))
+
+    def test_string_values(self):
+        original = {"state_delta": {"key": "value"}, "artifact_delta": {}}
+        self.assertEqual(self._round_trip(original), original)
+
+    def test_nested_dict(self):
+        original = {
+            "state_delta": {
+                "user_prefs": {"theme": "dark", "lang": "en"},
+                "counter": 42,
+            },
+            "artifact_delta": {"files": ["a.txt", "b.txt"]},
+        }
+        self.assertEqual(self._round_trip(original), original)
+
+    def test_none_and_bool(self):
+        original = {
+            "skip_summarization": True,
+            "requested_auth_configs": None,
+            "escalate": False,
+        }
+        self.assertEqual(self._round_trip(original), original)
+
+    def test_empty_dict(self):
+        self.assertEqual(self._round_trip({}), {})
+
+
+class TestEnvVarFallback(unittest.TestCase):
+    """ADK_ALLOW_UNSAFE_V0_PICKLE=1 must bypass RestrictedUnpickler."""
+
+    _ENV_KEY = "ADK_ALLOW_UNSAFE_V0_PICKLE"
+    _PAYLOAD = _make_global_payload("collections", "Counter")
+
+    def test_blocked_without_env_var(self):
+        old = os.environ.pop(self._ENV_KEY, None)
+        try:
+            with self.assertRaises(pickle.UnpicklingError):
+                safe_loads(self._PAYLOAD)
+        finally:
+            if old is not None:
+                os.environ[self._ENV_KEY] = old
+
+    def test_allowed_with_env_var(self):
+        old = os.environ.get(self._ENV_KEY)
+        try:
+            os.environ[self._ENV_KEY] = "1"
+            from collections import Counter
+            result = safe_loads(self._PAYLOAD)
+            self.assertIsInstance(result, Counter)
+        finally:
+            if old is None:
+                os.environ.pop(self._ENV_KEY, None)
+            else:
+                os.environ[self._ENV_KEY] = old
+
+
+if __name__ == "__main__":
+    unittest.main()