diff --git a/src/crawlee/_utils/file.py b/src/crawlee/_utils/file.py
index b3ee5662f4..7a9e13be28 100644
--- a/src/crawlee/_utils/file.py
+++ b/src/crawlee/_utils/file.py
@@ -60,6 +60,37 @@ def _write_file(path: Path, data: str | bytes) -> None:
             raise
 
 
+def validate_subdirectory(base_dir: Path, subdirectory: str) -> Path:
+    """Resolve a storage subdirectory inside a base directory.
+
+    Joins `subdirectory` onto `base_dir` and verifies that the result stays inside `base_dir`, so a storage
+    name or alias always maps to a directory under the storage directory rather than somewhere else (e.g. a
+    value containing `..` or an absolute path).
+
+    Args:
+        base_dir: The base storage directory (e.g. the `key_value_stores` directory).
+        subdirectory: The storage name or alias to use as the subdirectory.
+
+    Returns:
+        The validated full path to the storage subdirectory.
+
+    Raises:
+        ValueError: If the resolved path would fall outside `base_dir`.
+    """
+    # Normalize lexically (no filesystem access), so symlinks are not followed and the check is deterministic.
+    base_resolved = Path(os.path.normpath(base_dir))
+    target_resolved = Path(os.path.normpath(base_dir / subdirectory))
+
+    # The target must be strictly inside the base directory - reject parent references and absolute paths.
+    if target_resolved == base_resolved or base_resolved not in target_resolved.parents:
+        raise ValueError(
+            f'Invalid storage name or alias "{subdirectory}". It must not contain path separators, parent '
+            f'directory references ("..") or absolute paths that resolve outside the storage directory.'
+        )
+
+    return target_resolved
+
+
 def infer_mime_type(value: Any) -> str:
     """Infer the MIME content type from the value.
 
diff --git a/src/crawlee/storage_clients/_file_system/_dataset_client.py b/src/crawlee/storage_clients/_file_system/_dataset_client.py
index 8fce7b4733..89d0435092 100644
--- a/src/crawlee/storage_clients/_file_system/_dataset_client.py
+++ b/src/crawlee/storage_clients/_file_system/_dataset_client.py
@@ -15,7 +15,7 @@
 from crawlee._consts import METADATA_FILENAME
 from crawlee._types import JsonSerializable
 from crawlee._utils.crypto import crypto_random_object_id
-from crawlee._utils.file import atomic_write, json_dumps
+from crawlee._utils.file import atomic_write, json_dumps, validate_subdirectory
 from crawlee._utils.raise_if_too_many_kwargs import raise_if_too_many_kwargs
 from crawlee.storage_clients._base import DatasetClient
 from crawlee.storage_clients.models import DatasetItemsListPage, DatasetMetadata
@@ -159,8 +159,7 @@ async def open(
 
         # Get a new instance by name or alias.
         else:
-            dataset_dir = Path(name) if name else Path(alias) if alias else Path('default')
-            path_to_dataset = dataset_base_path / dataset_dir
+            path_to_dataset = validate_subdirectory(dataset_base_path, name or alias or 'default')
             path_to_metadata = path_to_dataset / METADATA_FILENAME
 
             # If the dataset directory exists, reconstruct the client from the metadata file.
diff --git a/src/crawlee/storage_clients/_file_system/_key_value_store_client.py b/src/crawlee/storage_clients/_file_system/_key_value_store_client.py
index 3a36a77074..984a88651f 100644
--- a/src/crawlee/storage_clients/_file_system/_key_value_store_client.py
+++ b/src/crawlee/storage_clients/_file_system/_key_value_store_client.py
@@ -15,7 +15,7 @@
 
 from crawlee._consts import METADATA_FILENAME
 from crawlee._utils.crypto import crypto_random_object_id
-from crawlee._utils.file import atomic_write, infer_mime_type, json_dumps
+from crawlee._utils.file import atomic_write, infer_mime_type, json_dumps, validate_subdirectory
 from crawlee._utils.raise_if_too_many_kwargs import raise_if_too_many_kwargs
 from crawlee.storage_clients._base import KeyValueStoreClient
 from crawlee.storage_clients.models import KeyValueStoreMetadata, KeyValueStoreRecord, KeyValueStoreRecordMetadata
@@ -157,8 +157,7 @@ async def open(
 
         # Get a new instance by name or alias.
         else:
-            kvs_dir = Path(name) if name else Path(alias) if alias else Path('default')
-            path_to_kvs = kvs_base_path / kvs_dir
+            path_to_kvs = validate_subdirectory(kvs_base_path, name or alias or 'default')
             path_to_metadata = path_to_kvs / METADATA_FILENAME
 
             # If the key-value store directory exists, reconstruct the client from the metadata file.
diff --git a/src/crawlee/storage_clients/_file_system/_request_queue_client.py b/src/crawlee/storage_clients/_file_system/_request_queue_client.py
index 4954d8a4d2..024a50b8a9 100644
--- a/src/crawlee/storage_clients/_file_system/_request_queue_client.py
+++ b/src/crawlee/storage_clients/_file_system/_request_queue_client.py
@@ -17,7 +17,7 @@
 from crawlee import Request
 from crawlee._consts import METADATA_FILENAME
 from crawlee._utils.crypto import crypto_random_object_id
-from crawlee._utils.file import atomic_write, json_dumps
+from crawlee._utils.file import atomic_write, json_dumps, validate_subdirectory
 from crawlee._utils.raise_if_too_many_kwargs import raise_if_too_many_kwargs
 from crawlee._utils.recoverable_state import RecoverableState
 from crawlee.storage_clients._base import RequestQueueClient
@@ -227,8 +227,7 @@ async def open(
 
         # Open an existing RQ by its name or alias, or create a new one if not found.
         else:
-            rq_dir = Path(name) if name else Path(alias) if alias else Path('default')
-            path_to_rq = rq_base_path / rq_dir
+            path_to_rq = validate_subdirectory(rq_base_path, name or alias or 'default')
             path_to_metadata = path_to_rq / METADATA_FILENAME
 
             # If the RQ directory exists, reconstruct the client from the metadata file.
diff --git a/src/crawlee/storages/_storage_instance_manager.py b/src/crawlee/storages/_storage_instance_manager.py
index 6e6c8c2359..05b6eeb081 100644
--- a/src/crawlee/storages/_storage_instance_manager.py
+++ b/src/crawlee/storages/_storage_instance_manager.py
@@ -10,7 +10,7 @@
 from crawlee._utils.raise_if_too_many_kwargs import raise_if_too_many_kwargs
 from crawlee.storage_clients._base import DatasetClient, KeyValueStoreClient, RequestQueueClient
 
-from ._utils import validate_storage_name
+from ._utils import validate_storage_alias, validate_storage_name
 
 if TYPE_CHECKING:
     from ._base import Storage
@@ -135,6 +135,10 @@ async def open_storage_instance(
             if name is not None:
                 validate_storage_name(name)
 
+            # Validate storage alias
+            if alias is not None:
+                validate_storage_alias(alias)
+
             # Acquire lock for this opener
             opener_lock_key = (cls, str(id or name or alias), storage_client_cache_key)
             if not (lock := self._opener_locks.get(opener_lock_key)):
diff --git a/src/crawlee/storages/_utils.py b/src/crawlee/storages/_utils.py
index 17e1fcc55c..2bfcab143b 100644
--- a/src/crawlee/storages/_utils.py
+++ b/src/crawlee/storages/_utils.py
@@ -9,3 +9,20 @@ def validate_storage_name(name: str | None) -> None:
             f'Invalid storage name "{name}". Name can only contain letters "a" through "z", the digits "0" through'
             '"9", and the hyphen ("-") but only in the middle of the string (e.g. "my-value-1")'
         )
+
+
+def validate_storage_alias(alias: str | None) -> None:
+    """Validate a storage alias that is used as an on-disk subdirectory name.
+
+    Unlike storage names, aliases may contain underscores and dots (e.g. the reserved `__default__` alias),
+    but must not contain path separators or parent-directory references, so an alias always maps to a single
+    directory under the storage directory.
+    """
+    if alias is None:
+        return
+
+    if not alias or '/' in alias or '\\' in alias or '\x00' in alias or alias in {'.', '..'}:
+        raise ValueError(
+            f'Invalid storage alias "{alias}". Alias must not be empty, contain path separators ("/", "\\") or '
+            f'null bytes, or be a directory reference (".", "..").'
+        )
diff --git a/tests/unit/_utils/test_file.py b/tests/unit/_utils/test_file.py
index c00618b600..91764d6df8 100644
--- a/tests/unit/_utils/test_file.py
+++ b/tests/unit/_utils/test_file.py
@@ -1,8 +1,14 @@
 from __future__ import annotations
 
 from datetime import datetime, timezone
+from typing import TYPE_CHECKING
 
-from crawlee._utils.file import json_dumps
+import pytest
+
+from crawlee._utils.file import json_dumps, validate_subdirectory
+
+if TYPE_CHECKING:
+    from pathlib import Path
 
 
 async def test_json_dumps() -> None:
@@ -11,3 +17,41 @@ async def test_json_dumps() -> None:
     assert await json_dumps('string') == '"string"'
     assert await json_dumps(123) == '123'
     assert await json_dumps(datetime(2022, 1, 1, tzinfo=timezone.utc)) == '"2022-01-01 00:00:00+00:00"'
+
+
+# Tests for validate_subdirectory (storage name/alias directory validation).
+
+
+@pytest.mark.parametrize(
+    'subdirectory',
+    [
+        pytest.param('my-store', id='simple'),
+        pytest.param('store_with_underscores', id='underscores'),
+        pytest.param('store.with.dots', id='dots'),
+        pytest.param('__default__', id='reserved-default'),
+        pytest.param('nested/inside', id='nested-but-contained'),
+    ],
+)
+def test_validate_subdirectory_accepts_safe_segments(tmp_path: Path, subdirectory: str) -> None:
+    base_dir = tmp_path / 'key_value_stores'
+    result = validate_subdirectory(base_dir, subdirectory)
+    # The resolved path must stay within the base directory.
+    assert result.parent == base_dir or base_dir in result.parents
+
+
+@pytest.mark.parametrize(
+    'subdirectory',
+    [
+        pytest.param('../outside', id='parent-ref'),
+        pytest.param('../../outside', id='deep-parent-ref'),
+        pytest.param('..', id='bare-parent'),
+        pytest.param('.', id='bare-current'),
+        pytest.param('a/../../outside', id='mixed-parent-ref'),
+        pytest.param('/etc/passwd', id='absolute-path'),
+        pytest.param('', id='empty'),
+    ],
+)
+def test_validate_subdirectory_rejects_invalid_segments(tmp_path: Path, subdirectory: str) -> None:
+    base_dir = tmp_path / 'key_value_stores'
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        validate_subdirectory(base_dir, subdirectory)
diff --git a/tests/unit/storage_clients/_file_system/test_fs_dataset_client.py b/tests/unit/storage_clients/_file_system/test_fs_dataset_client.py
index 3276ba2f0b..d7d2b4d64d 100644
--- a/tests/unit/storage_clients/_file_system/test_fs_dataset_client.py
+++ b/tests/unit/storage_clients/_file_system/test_fs_dataset_client.py
@@ -51,6 +51,33 @@ async def test_file_and_directory_creation(configuration: Configuration) -> None
     await client.drop()
 
 
+@pytest.mark.parametrize(
+    'invalid_value',
+    [
+        pytest.param('../outside', id='parent-ref'),
+        pytest.param('..', id='bare-parent'),
+        pytest.param('/abs/outside', id='absolute-path'),
+    ],
+)
+async def test_open_rejects_invalid_name_or_alias(
+    configuration: Configuration, tmp_path: Path, invalid_value: str
+) -> None:
+    """The low-level client must reject names/aliases that resolve outside the storage directory.
+
+    This covers direct usage of the storage client, which bypasses the high-level validation.
+    """
+    storage_client = FileSystemStorageClient()
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_dataset_client(alias=invalid_value, configuration=configuration)
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_dataset_client(name=invalid_value, configuration=configuration)
+
+    # Nothing should have been written outside the configured storage directory.
+    assert not (tmp_path / 'outside').exists()
+
+
 async def test_file_persistence_and_content_verification(dataset_client: FileSystemDatasetClient) -> None:
     """Test that data is properly persisted to files with correct content."""
     item = {'key': 'value', 'number': 42}
diff --git a/tests/unit/storage_clients/_file_system/test_fs_kvs_client.py b/tests/unit/storage_clients/_file_system/test_fs_kvs_client.py
index 5f2ae15da0..6866f59d05 100644
--- a/tests/unit/storage_clients/_file_system/test_fs_kvs_client.py
+++ b/tests/unit/storage_clients/_file_system/test_fs_kvs_client.py
@@ -49,6 +49,33 @@ async def test_file_and_directory_creation(configuration: Configuration) -> None
     await client.drop()
 
 
+@pytest.mark.parametrize(
+    'invalid_value',
+    [
+        pytest.param('../outside', id='parent-ref'),
+        pytest.param('..', id='bare-parent'),
+        pytest.param('/abs/outside', id='absolute-path'),
+    ],
+)
+async def test_open_rejects_invalid_name_or_alias(
+    configuration: Configuration, tmp_path: Path, invalid_value: str
+) -> None:
+    """The low-level client must reject names/aliases that resolve outside the storage directory.
+
+    This covers direct usage of the storage client, which bypasses the high-level validation.
+    """
+    storage_client = FileSystemStorageClient()
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_kvs_client(alias=invalid_value, configuration=configuration)
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_kvs_client(name=invalid_value, configuration=configuration)
+
+    # Nothing should have been written outside the configured storage directory.
+    assert not (tmp_path / 'outside').exists()
+
+
 async def test_value_file_creation_and_content(kvs_client: FileSystemKeyValueStoreClient) -> None:
     """Test that values are properly persisted to files with correct content and metadata."""
     test_key = 'test-key'
diff --git a/tests/unit/storage_clients/_file_system/test_fs_rq_client.py b/tests/unit/storage_clients/_file_system/test_fs_rq_client.py
index 275665d9d5..a3641f60bf 100644
--- a/tests/unit/storage_clients/_file_system/test_fs_rq_client.py
+++ b/tests/unit/storage_clients/_file_system/test_fs_rq_client.py
@@ -51,6 +51,33 @@ async def test_file_and_directory_creation() -> None:
     await client.drop()
 
 
+@pytest.mark.parametrize(
+    'invalid_value',
+    [
+        pytest.param('../outside', id='parent-ref'),
+        pytest.param('..', id='bare-parent'),
+        pytest.param('/abs/outside', id='absolute-path'),
+    ],
+)
+async def test_open_rejects_invalid_name_or_alias(
+    configuration: Configuration, tmp_path: Path, invalid_value: str
+) -> None:
+    """The low-level client must reject names/aliases that resolve outside the storage directory.
+
+    This covers direct usage of the storage client, which bypasses the high-level validation.
+    """
+    storage_client = FileSystemStorageClient()
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_rq_client(alias=invalid_value, configuration=configuration)
+
+    with pytest.raises(ValueError, match='Invalid storage name or alias'):
+        await storage_client.create_rq_client(name=invalid_value, configuration=configuration)
+
+    # Nothing should have been written outside the configured storage directory.
+    assert not (tmp_path / 'outside').exists()
+
+
 async def test_request_file_persistence(rq_client: FileSystemRequestQueueClient) -> None:
     """Test that requests are properly persisted to files."""
     requests = [
diff --git a/tests/unit/storages/test_dataset.py b/tests/unit/storages/test_dataset.py
index 3b0a8e1d6e..1d55e250dc 100644
--- a/tests/unit/storages/test_dataset.py
+++ b/tests/unit/storages/test_dataset.py
@@ -1078,6 +1078,8 @@ async def test_name_default_not_allowed(storage_client: StorageClient) -> None:
         pytest.param('name with spaces', False, id='spaces'),
         pytest.param('-test', False, id='dashes start'),
         pytest.param('test-', False, id='dashes end'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('with/slash', False, id='slash'),
     ],
 )
 async def test_validate_name(storage_client: StorageClient, name: str, *, is_valid: bool) -> None:
@@ -1092,6 +1094,31 @@ async def test_validate_name(storage_client: StorageClient, name: str, *, is_val
             await Dataset.open(name=name, storage_client=storage_client)
 
 
+@pytest.mark.parametrize(
+    ('alias', 'is_valid'),
+    [
+        pytest.param('valid-alias', True, id='dashes'),
+        pytest.param('alias_with_underscores', True, id='underscores'),
+        pytest.param('alias.with.dots', True, id='dots'),
+        pytest.param('CamelCaseAlias', True, id='mixed-case'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('..', False, id='bare-parent'),
+        pytest.param('.', False, id='bare-current'),
+        pytest.param('nested/alias', False, id='slash'),
+        pytest.param('back\\slash', False, id='backslash'),
+    ],
+)
+async def test_validate_alias(storage_client: StorageClient, alias: str, *, is_valid: bool) -> None:
+    """Test alias validation logic, including rejection of values that would resolve outside the storage dir."""
+    if is_valid:
+        # Should not raise.
+        dataset = await Dataset.open(alias=alias, storage_client=storage_client)
+        await dataset.drop()
+    else:
+        with pytest.raises(ValueError, match=r'Invalid storage alias'):
+            await Dataset.open(alias=alias, storage_client=storage_client)
+
+
 async def test_record_with_noascii_chars(dataset: Dataset) -> None:
     """Test handling record with non-ASCII characters."""
     init_value = {
diff --git a/tests/unit/storages/test_key_value_store.py b/tests/unit/storages/test_key_value_store.py
index 5b789d2843..42467f3c5f 100644
--- a/tests/unit/storages/test_key_value_store.py
+++ b/tests/unit/storages/test_key_value_store.py
@@ -1080,6 +1080,8 @@ async def test_name_default_not_allowed(storage_client: StorageClient) -> None:
         pytest.param('name with spaces', False, id='spaces'),
         pytest.param('-test', False, id='dashes start'),
         pytest.param('test-', False, id='dashes end'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('with/slash', False, id='slash'),
     ],
 )
 async def test_validate_name(storage_client: StorageClient, name: str, *, is_valid: bool) -> None:
@@ -1094,6 +1096,31 @@ async def test_validate_name(storage_client: StorageClient, name: str, *, is_val
             await KeyValueStore.open(name=name, storage_client=storage_client)
 
 
+@pytest.mark.parametrize(
+    ('alias', 'is_valid'),
+    [
+        pytest.param('valid-alias', True, id='dashes'),
+        pytest.param('alias_with_underscores', True, id='underscores'),
+        pytest.param('alias.with.dots', True, id='dots'),
+        pytest.param('CamelCaseAlias', True, id='mixed-case'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('..', False, id='bare-parent'),
+        pytest.param('.', False, id='bare-current'),
+        pytest.param('nested/alias', False, id='slash'),
+        pytest.param('back\\slash', False, id='backslash'),
+    ],
+)
+async def test_validate_alias(storage_client: StorageClient, alias: str, *, is_valid: bool) -> None:
+    """Test alias validation logic, including rejection of values that would resolve outside the storage dir."""
+    if is_valid:
+        # Should not raise.
+        kvs = await KeyValueStore.open(alias=alias, storage_client=storage_client)
+        await kvs.drop()
+    else:
+        with pytest.raises(ValueError, match=r'Invalid storage alias'):
+            await KeyValueStore.open(alias=alias, storage_client=storage_client)
+
+
 @pytest.mark.parametrize(
     'tested_storage_client_class',
     [
diff --git a/tests/unit/storages/test_request_queue.py b/tests/unit/storages/test_request_queue.py
index 56704ebbed..9df49ec79f 100644
--- a/tests/unit/storages/test_request_queue.py
+++ b/tests/unit/storages/test_request_queue.py
@@ -1471,6 +1471,8 @@ async def test_name_default_not_allowed(storage_client: StorageClient) -> None:
         pytest.param('name with spaces', False, id='spaces'),
         pytest.param('-test', False, id='dashes start'),
         pytest.param('test-', False, id='dashes end'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('with/slash', False, id='slash'),
     ],
 )
 async def test_validate_name(storage_client: StorageClient, name: str, *, is_valid: bool) -> None:
@@ -1485,6 +1487,31 @@ async def test_validate_name(storage_client: StorageClient, name: str, *, is_val
             await RequestQueue.open(name=name, storage_client=storage_client)
 
 
+@pytest.mark.parametrize(
+    ('alias', 'is_valid'),
+    [
+        pytest.param('valid-alias', True, id='dashes'),
+        pytest.param('alias_with_underscores', True, id='underscores'),
+        pytest.param('alias.with.dots', True, id='dots'),
+        pytest.param('CamelCaseAlias', True, id='mixed-case'),
+        pytest.param('../outside', False, id='parent-ref'),
+        pytest.param('..', False, id='bare-parent'),
+        pytest.param('.', False, id='bare-current'),
+        pytest.param('nested/alias', False, id='slash'),
+        pytest.param('back\\slash', False, id='backslash'),
+    ],
+)
+async def test_validate_alias(storage_client: StorageClient, alias: str, *, is_valid: bool) -> None:
+    """Test alias validation logic, including rejection of values that would resolve outside the storage dir."""
+    if is_valid:
+        # Should not raise.
+        rq = await RequestQueue.open(alias=alias, storage_client=storage_client)
+        await rq.drop()
+    else:
+        with pytest.raises(ValueError, match=r'Invalid storage alias'):
+            await RequestQueue.open(alias=alias, storage_client=storage_client)
+
+
 async def test_reclaim_request_with_change_state(rq: RequestQueue) -> None:
     """Test reclaiming a request and changing its state."""
     # Add a request