diff --git a/src/google/adk/code_executors/container_code_executor.py b/src/google/adk/code_executors/container_code_executor.py
index d6a78d4d26..b1943924a6 100644
--- a/src/google/adk/code_executors/container_code_executor.py
+++ b/src/google/adk/code_executors/container_code_executor.py
@@ -37,6 +37,15 @@
 class ContainerCodeExecutor(BaseCodeExecutor):
   """A code executor that uses a custom container to execute code.
 
+  Security note: this executor runs model-generated code, which may be
+  influenced by untrusted input (e.g. via prompt injection). By default the
+  container is started with networking disabled and all Linux capabilities
+  dropped so that the executed code cannot reach the network (including the
+  cloud metadata endpoint at ``169.254.169.254``) or escalate privileges. For
+  stronger, kernel-level isolation of untrusted code prefer
+  ``GkeCodeExecutor`` (gVisor) or a managed executor
+  (``VertexAiCodeExecutor`` / ``AgentEngineSandboxCodeExecutor``).
+
   Attributes:
     base_url: Optional. The base url of the user hosted Docker client.
     image: The tag of the predefined image or custom image to run on the
@@ -44,6 +53,9 @@ class ContainerCodeExecutor(BaseCodeExecutor):
     docker_path: The path to the directory containing the Dockerfile. If set,
       build the image from the dockerfile path instead of using the predefined
       image. Either docker_path or image must be set.
+    network_disabled: Whether to start the container with networking disabled.
+      Defaults to True. Set to False only if the executed code must make
+      network requests and you trust it.
   """
 
   base_url: Optional[str] = None
@@ -64,6 +76,17 @@ class ContainerCodeExecutor(BaseCodeExecutor):
   predefined image. Either docker_path or image must be set.
   """
 
+  network_disabled: bool = True
+  """
+  Whether to start the code execution container with networking disabled.
+
+  Defaults to True so that untrusted, model-generated code cannot reach the
+  network -- in particular the cloud metadata endpoint at 169.254.169.254
+  (which can yield the host's service-account credentials), internal services,
+  or arbitrary exfiltration destinations. Set to False only if the executed
+  code must make network requests and you trust it.
+  """
+
   # Overrides the BaseCodeExecutor attribute: this executor cannot be stateful.
   stateful: bool = Field(default=False, frozen=True, exclude=True)
 
@@ -183,6 +206,13 @@ def __init_container(self):
         image=self.image,
         detach=True,
         tty=True,
+        # Harden the sandbox for untrusted, model-generated code: no network
+        # (blocks metadata/SSRF/exfil), drop all Linux capabilities, and
+        # forbid privilege escalation. Networking can be re-enabled via
+        # `network_disabled=False` when the executed code is trusted.
+        network_disabled=self.network_disabled,
+        cap_drop=['ALL'],
+        security_opt=['no-new-privileges'],
     )
     logger.info('Container %s started.', self._container.id)
 
diff --git a/tests/unittests/code_executors/test_container_code_executor.py b/tests/unittests/code_executors/test_container_code_executor.py
new file mode 100644
index 0000000000..a26b02fdd2
--- /dev/null
+++ b/tests/unittests/code_executors/test_container_code_executor.py
@@ -0,0 +1,56 @@
+# Copyright 2025 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 the ContainerCodeExecutor container hardening defaults."""
+
+from unittest import mock
+
+from google.adk.code_executors.container_code_executor import ContainerCodeExecutor
+
+
+def _mock_docker_client():
+  """Returns a mock Docker client whose container passes python verification."""
+  client = mock.MagicMock()
+  container = mock.MagicMock()
+  # `_verify_python_installation` runs `exec_run(['which', 'python3'])` and
+  # checks `exit_code == 0`.
+  container.exec_run.return_value = mock.MagicMock(exit_code=0)
+  client.containers.run.return_value = container
+  return client
+
+
+@mock.patch('google.adk.code_executors.container_code_executor.docker')
+def test_container_is_hardened_by_default(mock_docker):
+  client = _mock_docker_client()
+  mock_docker.from_env.return_value = client
+
+  ContainerCodeExecutor(image='test-image')
+
+  _, kwargs = client.containers.run.call_args
+  # Untrusted model-generated code must not be able to reach the network
+  # (e.g. the cloud metadata endpoint) or escalate privileges by default.
+  assert kwargs['network_disabled'] is True
+  assert kwargs['cap_drop'] == ['ALL']
+  assert kwargs['security_opt'] == ['no-new-privileges']
+
+
+@mock.patch('google.adk.code_executors.container_code_executor.docker')
+def test_container_network_can_be_explicitly_enabled(mock_docker):
+  client = _mock_docker_client()
+  mock_docker.from_env.return_value = client
+
+  ContainerCodeExecutor(image='test-image', network_disabled=False)
+
+  _, kwargs = client.containers.run.call_args
+  assert kwargs['network_disabled'] is False