gh-121999: Change default tarfile filter to 'data' (GH-122002)

Co-authored-by: Tomas R <tomas.roun8@gmail.com>
Co-authored-by: Scott Odle <scott@sjodle.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>

Doc/library/shutil.rst

@@ -706,11 +706,9 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
 
    The keyword-only *filter* argument is passed to the underlying unpacking
    function. For zip files, *filter* is not accepted.
-   For tar files, it is recommended to set it to ``'data'``,
+   For tar files, it is recommended to use ``'data'`` (default since Python
-   unless using features specific to tar and UNIX-like filesystems.
+   3.14), unless using features specific to tar and UNIX-like filesystems.
    (See :ref:`tarfile-extraction-filter` for details.)
-   The ``'data'`` filter will become the default for tar files
-   in Python 3.14.
 
    .. audit-event:: shutil.unpack_archive filename,extract_dir,format shutil.unpack_archive
 
@@ -721,6 +719,12 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
       the *extract_dir* argument, e.g. members that have absolute filenames
       starting with "/" or filenames with two dots "..".
 
+      Since Python 3.14, the defaults for both built-in formats (zip and tar
+      files) will prevent the most dangerous of such security issues,
+      but will not prevent *all* unintended behavior.
+      Read the :ref:`tarfile-further-verification`
+      section for tar-specific details.
+
    .. versionchanged:: 3.7
       Accepts a :term:`path-like object` for *filename* and *extract_dir*.
 

Doc/library/tarfile.rst

@@ -40,9 +40,12 @@ Some facts and figures:
    Archives are extracted using a :ref:`filter <tarfile-extraction-filter>`,
    which makes it possible to either limit surprising/dangerous features,
    or to acknowledge that they are expected and the archive is fully trusted.
-   By default, archives are fully trusted, but this default is deprecated
-   and slated to change in Python 3.14.
 
+.. versionchanged:: 3.14
+   Set the default extraction filter to :func:`data <data_filter>`,
+   which disallows some dangerous features such as links to absolute paths
+   or paths outside of the destination. Previously, the filter strategy
+   was equivalent to :func:`fully_trusted <fully_trusted_filter>`.
 
 .. function:: open(name=None, mode='r', fileobj=None, bufsize=10240, **kwargs)
 
@@ -495,18 +498,18 @@ be finalized; only the internally used file object will be closed. See the
    The *filter* argument specifies how ``members`` are modified or rejected
    before extraction.
    See :ref:`tarfile-extraction-filter` for details.
-   It is recommended to set this explicitly depending on which *tar* features
+   It is recommended to set this explicitly only if specific *tar* features
-   you need to support.
+   are required, or as ``filter='data'`` to support Python versions with a less
+   secure default (3.13 and lower).
 
    .. warning::
 
       Never extract archives from untrusted sources without prior inspection.
-      It is possible that files are created outside of *path*, e.g. members
-      that have absolute filenames starting with ``"/"`` or filenames with two
-      dots ``".."``.
 
-      Set ``filter='data'`` to prevent the most dangerous security issues,
+      Since Python 3.14, the default (:func:`data <data_filter>`) will prevent
-      and read the :ref:`tarfile-extraction-filter` section for details.
+      the most dangerous security issues.
+      However, it will not prevent *all* unintended or insecure behavior.
+      Read the :ref:`tarfile-extraction-filter` section for details.
 
    .. versionchanged:: 3.5
       Added the *numeric_owner* parameter.
@@ -517,6 +520,9 @@ be finalized; only the internally used file object will be closed. See the
    .. versionchanged:: 3.12
       Added the *filter* parameter.
 
+   .. versionchanged:: 3.14
+      The *filter* parameter now defaults to ``'data'``.
+
 
 .. method:: TarFile.extract(member, path="", set_attrs=True, *, numeric_owner=False, filter=None)
 
@@ -536,10 +542,8 @@ be finalized; only the internally used file object will be closed. See the
 
    .. warning::
 
-      See the warning for :meth:`extractall`.
+      Never extract archives from untrusted sources without prior inspection.
-
+      See the warning for :meth:`extractall` for details.
-      Set ``filter='data'`` to prevent the most dangerous security issues,
-      and read the :ref:`tarfile-extraction-filter` section for details.
 
    .. versionchanged:: 3.2
       Added the *set_attrs* parameter.
@@ -602,14 +606,8 @@ be finalized; only the internally used file object will be closed. See the
    String names are not allowed for this attribute, unlike the *filter*
    argument to :meth:`~TarFile.extract`.
 
-   If ``extraction_filter`` is ``None`` (the default),
+   If ``extraction_filter`` is ``None`` (the default), extraction methods
-   calling an extraction method without a *filter* argument will raise a
+   will use the :func:`data <data_filter>` filter by default.
-   ``DeprecationWarning``,
-   and fall back to the :func:`fully_trusted <fully_trusted_filter>` filter,
-   whose dangerous behavior matches previous versions of Python.
-
-   In Python 3.14+, leaving ``extraction_filter=None`` will cause
-   extraction methods to use the :func:`data <data_filter>` filter by default.
 
    The attribute may be set on instances or overridden in subclasses.
    It also is possible to set it on the ``TarFile`` class itself to set a
@@ -619,6 +617,14 @@ be finalized; only the internally used file object will be closed. See the
    To set a global default this way, a filter function needs to be wrapped in
    :func:`staticmethod()` to prevent injection of a ``self`` argument.
 
+   .. versionchanged:: 3.14
+
+      The default filter is set to :func:`data <data_filter>`,
+      which disallows some dangerous features such as links to absolute paths
+      or paths outside of the destination.
+      Previously, the default was equivalent to
+      :func:`fully_trusted <fully_trusted_filter>`.
+
 .. method:: TarFile.add(name, arcname=None, recursive=True, *, filter=None)
 
    Add the file *name* to the archive. *name* may be any type of file
@@ -969,6 +975,12 @@ In most cases, the full functionality is not needed.
 Therefore, *tarfile* supports extraction filters: a mechanism to limit
 functionality, and thus mitigate some of the security issues.
 
+.. warning::
+
+   None of the available filters blocks *all* dangerous archive features.
+   Never extract archives from untrusted sources without prior inspection.
+   See also :ref:`tarfile-further-verification`.
+
 .. seealso::
 
    :pep:`706`
@@ -992,12 +1004,13 @@ can be:
 
 * ``None`` (default): Use :attr:`TarFile.extraction_filter`.
 
-  If that is also ``None`` (the default), raise a ``DeprecationWarning``,
+  If that is also ``None`` (the default), the ``'data'`` filter will be used.
-  and fall back to the ``'fully_trusted'`` filter, whose dangerous behavior
-  matches previous versions of Python.
 
-  In Python 3.14, the ``'data'`` filter will become the default instead.
+   .. versionchanged:: 3.14
-  It's possible to switch earlier; see :attr:`TarFile.extraction_filter`.
+
+      The default filter is set to :func:`data <data_filter>`.
+      Previously, the default was equivalent to
+      :func:`fully_trusted <fully_trusted_filter>`.
 
 * A callable which will be called for each extracted member with a
   :ref:`TarInfo <tarinfo-objects>` describing the member and the destination
@@ -1080,6 +1093,9 @@ reused in custom filters:
 
   Return the modified ``TarInfo`` member.
 
+  Note that this filter does not block *all* dangerous archive features.
+  See :ref:`tarfile-further-verification`  for details.
+
 
 .. _tarfile-extraction-refuse:
 
@@ -1093,6 +1109,8 @@ With ``errorlevel=0`` the error will be logged and the member will be skipped,
 but extraction will continue.
 
 
+.. _tarfile-further-verification:
+
 Hints for further verification
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -1110,9 +1128,10 @@ Here is an incomplete list of things to consider:
   disk, memory and CPU usage.
 * Check filenames against an allow-list of characters
   (to filter out control characters, confusables, foreign path separators,
-  etc.).
+  and so on).
 * Check that filenames have expected extensions (discouraging files that
-  execute when you “click on them”, or extension-less files like Windows special device names).
+  execute when you “click on them”, or extension-less files like Windows
+  special device names).
 * Limit the number of extracted files, total size of extracted data,
   filename length (including symlink length), and size of individual files.
 * Check for files that would be shadowed on case-insensitive filesystems.

Lib/tarfile.py

@@ -2248,13 +2248,7 @@ class TarFile(object):
         if filter is None:
             filter = self.extraction_filter
             if filter is None:
-                import warnings
+                return data_filter
-                warnings.warn(
-                    'Python 3.14 will, by default, filter extracted tar '
-                    + 'archives and reject files or modify their metadata. '
-                    + 'Use the filter argument to control this behavior.',
-                    DeprecationWarning, stacklevel=3)
-                return fully_trusted_filter
             if isinstance(filter, str):
                 raise TypeError(
                     'String names are not supported for '

Lib/test/test_shutil.py

@@ -2145,9 +2145,6 @@ class TestArchives(BaseTest, unittest.TestCase):
     def check_unpack_tarball(self, format):
         self.check_unpack_archive(format, filter='fully_trusted')
         self.check_unpack_archive(format, filter='data')
-        with warnings_helper.check_warnings(
-                ('Python 3.14', DeprecationWarning)):
-            self.check_unpack_archive(format)
 
     def test_unpack_archive_tar(self):
         self.check_unpack_tarball('tar')

Lib/test/test_tarfile.py

@@ -722,6 +722,24 @@ class MiscReadTestBase(CommonReadTest):
             tar.close()
             os_helper.rmtree(DIR)
 
+    @staticmethod
+    def test_extractall_default_filter():
+        # Test that the default filter is now "data", and the other filter types are not used.
+        DIR = pathlib.Path(TEMPDIR) / "extractall_default_filter"
+        with (
+            os_helper.temp_dir(DIR),
+            tarfile.open(tarname, encoding="iso8859-1") as tar,
+            unittest.mock.patch("tarfile.data_filter", wraps=tarfile.data_filter) as mock_data_filter,
+            unittest.mock.patch("tarfile.tar_filter", wraps=tarfile.tar_filter) as mock_tar_filter,
+            unittest.mock.patch("tarfile.fully_trusted_filter", wraps=tarfile.fully_trusted_filter) as mock_ft_filter
+        ):
+            directories = [t for t in tar if t.isdir()]
+            tar.extractall(DIR, directories)
+
+            mock_data_filter.assert_called()
+            mock_ft_filter.assert_not_called()
+            mock_tar_filter.assert_not_called()
+
     @os_helper.skip_unless_working_chmod
     def test_extract_directory(self):
         dirtype = "ustar/dirtype"
@@ -738,31 +756,6 @@ class MiscReadTestBase(CommonReadTest):
         finally:
             os_helper.rmtree(DIR)
 
-    def test_deprecation_if_no_filter_passed_to_extractall(self):
-        DIR = pathlib.Path(TEMPDIR) / "extractall"
-        with (
-            os_helper.temp_dir(DIR),
-            tarfile.open(tarname, encoding="iso8859-1") as tar
-        ):
-            directories = [t for t in tar if t.isdir()]
-            with self.assertWarnsRegex(DeprecationWarning, "Use the filter argument") as cm:
-                tar.extractall(DIR, directories)
-            # check that the stacklevel of the deprecation warning is correct:
-            self.assertEqual(cm.filename, __file__)
-
-    def test_deprecation_if_no_filter_passed_to_extract(self):
-        dirtype = "ustar/dirtype"
-        DIR = pathlib.Path(TEMPDIR) / "extractall"
-        with (
-            os_helper.temp_dir(DIR),
-            tarfile.open(tarname, encoding="iso8859-1") as tar
-        ):
-            tarinfo = tar.getmember(dirtype)
-            with self.assertWarnsRegex(DeprecationWarning, "Use the filter argument") as cm:
-                tar.extract(tarinfo, path=DIR)
-            # check that the stacklevel of the deprecation warning is correct:
-            self.assertEqual(cm.filename, __file__)
-
     def test_extractall_pathlike_dir(self):
         DIR = os.path.join(TEMPDIR, "extractall")
         with os_helper.temp_dir(DIR), \
@@ -4011,15 +4004,6 @@ class TestExtractionFilters(unittest.TestCase):
                 self.assertIs(filtered.name, tarinfo.name)
                 self.assertIs(filtered.type, tarinfo.type)
 
-    def test_default_filter_warns(self):
-        """Ensure the default filter warns"""
-        with ArchiveMaker() as arc:
-            arc.add('foo')
-        with warnings_helper.check_warnings(
-                ('Python 3.14', DeprecationWarning)):
-            with self.check_context(arc.open(), None):
-                self.expect_file('foo')
-
     def test_change_default_filter_on_instance(self):
         tar = tarfile.TarFile(tarname, 'r')
         def strict_filter(tarinfo, path):

Misc/NEWS.d/next/Core_and_Builtins/2024-07-18-21-19-04.gh-issue-121999.8IBbTK.rst

@@ -0,0 +1,2 @@
+The default extraction filter for the :mod:`tarfile` module is now
+set to :func:`'data' <tarfile.data_filter>`.