diff --git a/mock_tests/test_grpc_config.py b/mock_tests/test_grpc_config.py
index e0626118c..4ac24626f 100644
--- a/mock_tests/test_grpc_config.py
+++ b/mock_tests/test_grpc_config.py
@@ -1,6 +1,7 @@
 from typing import Any, List, Tuple
 from unittest.mock import MagicMock
 
+import certifi
 import grpc
 import pytest
 
@@ -47,18 +48,36 @@ def test_grpc_config_channel_options() -> None:
 
 
 def test_secure_channel_default_credentials(
-    secure_params: ConnectionParams, mock_grpc: MagicMock, mock_ssl_creds: MagicMock
+    secure_params: ConnectionParams,
+    mock_grpc: MagicMock,
+    mock_ssl_creds: MagicMock,
+    monkeypatch: pytest.MonkeyPatch,
 ) -> None:
+    monkeypatch.delenv("GRPC_DEFAULT_SSL_ROOTS_FILE_PATH", raising=False)
     mock_channel = MagicMock()
     mock_grpc.secure_channel.return_value = mock_channel
 
     result = secure_params._grpc_channel(proxies={}, grpc_msg_size=None, is_async=False)
 
-    mock_ssl_creds.assert_called_once_with()
-    mock_grpc.secure_channel.assert_called_once()
+    with open(certifi.where(), "rb") as f:
+        mock_ssl_creds.assert_called_once_with(root_certificates=f.read())
+    assert mock_grpc.secure_channel.call_args.kwargs["credentials"] is mock_ssl_creds.return_value
     assert result is mock_channel
 
 
+def test_secure_channel_roots_file_env_overrides_certifi(
+    secure_params: ConnectionParams,
+    mock_grpc: MagicMock,
+    mock_ssl_creds: MagicMock,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("GRPC_DEFAULT_SSL_ROOTS_FILE_PATH", "/etc/ssl/corp-roots.pem")
+
+    secure_params._grpc_channel(proxies={}, grpc_msg_size=None, is_async=False)
+
+    mock_ssl_creds.assert_called_once_with()
+
+
 def test_insecure_channel_no_config(
     insecure_params: ConnectionParams, mock_grpc: MagicMock
 ) -> None:
diff --git a/setup.cfg b/setup.cfg
index 958118ed2..b964b7ef3 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,6 +35,9 @@ platforms = any
 include_package_data = True
 install_requires =
     httpx>=0.26.0,<0.29.0
+    # CA bundle for both REST (via httpx) and gRPC. 2026.10.19 drops the emSign ECC
+    # Root CA - G3, whose intermediates' private keys were compromised in October 2026.
+    certifi>=2026.10.19
     validators>=0.34.0,<1.0.0
     authlib>=1.7.1,<2.0.0
     pydantic>=2.12.0,<3.0.0
diff --git a/weaviate/config.py b/weaviate/config.py
index d4ce8533c..30969d83e 100644
--- a/weaviate/config.py
+++ b/weaviate/config.py
@@ -85,6 +85,7 @@ class GrpcConfig(BaseModel):
     To provide your own `channel_options`, supply a list of tuples where each tuple contains the name of the gRPC channel option and its corresponding value.
         [Reference](https://grpc.github.io/grpc/python/glossary.html#term-channel_arguments)
 
+    Without `credentials`, secure channels trust certifi's CA bundle, or the roots file named by the `GRPC_DEFAULT_SSL_ROOTS_FILE_PATH` environment variable if it is set.
     To provide your own `credentials`, use the `ssl_channel_credentials()` function from the `grpc` library to build a `ChannelCredentials` object.
         [Reference](https://grpc.github.io/grpc/python/grpc.html#grpc.ssl_channel_credentials)
 
diff --git a/weaviate/connect/base.py b/weaviate/connect/base.py
index 5ac4689d8..8568985a7 100644
--- a/weaviate/connect/base.py
+++ b/weaviate/connect/base.py
@@ -2,6 +2,7 @@
 from typing import Any, Dict, Mapping, Optional, Sequence, Tuple, TypeVar, Union, cast
 from urllib.parse import urlparse
 
+import certifi
 import grpc  # type: ignore
 from grpc import Channel as SyncChannel
 from grpc import ssl_channel_credentials
@@ -30,6 +31,18 @@ def _grpc_web_shim_active() -> bool:
     return getattr(grpc, "__weaviate_client_web_shim__", False) is True
 
 
+def _default_grpc_credentials() -> grpc.ChannelCredentials:
+    """SSL credentials trusting certifi's CA bundle, the same one httpx uses for REST.
+
+    grpcio's bundled roots only change with a grpcio release, so a CA distrust reaches
+    certifi first. A roots file set via GRPC_DEFAULT_SSL_ROOTS_FILE_PATH still wins.
+    """
+    if os.environ.get("GRPC_DEFAULT_SSL_ROOTS_FILE_PATH"):
+        return ssl_channel_credentials()
+    with open(certifi.where(), "rb") as f:
+        return ssl_channel_credentials(root_certificates=f.read())
+
+
 class ProtocolParams(BaseModel):
     host: str
     port: int
@@ -201,7 +214,7 @@ def _grpc_channel(
             if grpc_config is not None and grpc_config.credentials is not None:
                 creds = grpc_config.credentials
             else:
-                creds = ssl_channel_credentials()
+                creds = _default_grpc_credentials()
             return mod.secure_channel(
                 target=self._grpc_target,
                 credentials=creds,