[2.2.x] Fixed CVE-2021-3281 -- Fixed potential directory-traversal via archive.extract().

Thanks Florian Apolloner, Shai Berger, and Simon Charette for reviews.

Thanks Wang Baohua for the report.

Backport of 05413afa8c18cdb978fcdf470e09f7a12b234a23 from master.

8 files changed, 51 insertions, 3 deletions

diff --git a/django/utils/archive.py b/django/utils/archive.py
index 5b9998f89c..f2f153a1fc 100644
--- a/django/utils/archive.py
+++ b/django/utils/archive.py
@@ -27,6 +27,8 @@ import stat
 import tarfile
 import zipfile
 
+from django.core.exceptions import SuspiciousOperation
+
 
 class ArchiveException(Exception):
     """
@@ -133,6 +135,13 @@ class BaseArchive:
                 return False
         return True
 
+    def target_filename(self, to_path, name):
+        target_path = os.path.abspath(to_path)
+        filename = os.path.abspath(os.path.join(target_path, name))
+        if not filename.startswith(target_path):
+            raise SuspiciousOperation("Archive contains invalid path: '%s'" % name)
+        return filename
+
     def extract(self):
         raise NotImplementedError('subclasses of BaseArchive must provide an extract() method')
 
@@ -155,7 +164,7 @@ class TarArchive(BaseArchive):
             name = member.name
             if leading:
                 name = self.split_leading_dir(name)[1]
-            filename = os.path.join(to_path, name)
+            filename = self.target_filename(to_path, name)
             if member.isdir():
                 if filename and not os.path.exists(filename):
                     os.makedirs(filename)
@@ -198,11 +207,13 @@ class ZipArchive(BaseArchive):
             info = self._archive.getinfo(name)
             if leading:
                 name = self.split_leading_dir(name)[1]
-            filename = os.path.join(to_path, name)
+            if not name:
+                continue
+            filename = self.target_filename(to_path, name)
             dirname = os.path.dirname(filename)
             if dirname and not os.path.exists(dirname):
                 os.makedirs(dirname)
-            if filename.endswith(('/', '\\')):
+            if name.endswith(('/', '\\')):
                 # A directory
                 if not os.path.exists(filename):
                     os.makedirs(filename)
diff --git a/docs/releases/2.2.18.txt b/docs/releases/2.2.18.txt
new file mode 100644
index 0000000000..45df4fb83c
--- /dev/null
+++ b/docs/releases/2.2.18.txt
@@ -0,0 +1,15 @@
+===========================
+Django 2.2.18 release notes
+===========================
+
+*February 1, 2021*
+
+Django 2.2.18 fixes a security issue with severity "low" in 2.2.17.
+
+CVE-2021-3281: Potential directory-traversal via ``archive.extract()``
+======================================================================
+
+The ``django.utils.archive.extract()`` function, used by
+:option:`startapp --template` and :option:`startproject --template`, allowed
+directory-traversal via an archive with absolute paths or relative paths with
+dot segments.
diff --git a/docs/releases/index.txt b/docs/releases/index.txt
index 247b69e797..67131ba1d8 100644
--- a/docs/releases/index.txt
+++ b/docs/releases/index.txt
@@ -25,6 +25,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   2.2.18
    2.2.17
    2.2.16
    2.2.15
diff --git a/tests/utils_tests/test_archive.py b/tests/utils_tests/test_archive.py
index d58d211ae5..ed7908df82 100644
--- a/tests/utils_tests/test_archive.py
+++ b/tests/utils_tests/test_archive.py
@@ -5,6 +5,8 @@ import sys
 import tempfile
 import unittest
 
+from django.core.exceptions import SuspiciousOperation
+from django.test import SimpleTestCase
 from django.utils.archive import Archive, extract
 
 TEST_DIR = os.path.join(os.path.dirname(__file__), 'archives')
@@ -87,3 +89,22 @@ class TestGzipTar(ArchiveTester, unittest.TestCase):
 
 class TestBzip2Tar(ArchiveTester, unittest.TestCase):
     archive = 'foobar.tar.bz2'
+
+
+class TestArchiveInvalid(SimpleTestCase):
+    def test_extract_function_traversal(self):
+        archives_dir = os.path.join(os.path.dirname(__file__), 'traversal_archives')
+        tests = [
+            ('traversal.tar', '..'),
+            ('traversal_absolute.tar', '/tmp/evil.py'),
+        ]
+        if sys.platform == 'win32':
+            tests += [
+                ('traversal_disk_win.tar', 'd:evil.py'),
+                ('traversal_disk_win.zip', 'd:evil.py'),
+            ]
+        msg = "Archive contains invalid path: '%s'"
+        for entry, invalid_path in tests:
+            with self.subTest(entry), tempfile.TemporaryDirectory() as tmpdir:
+                with self.assertRaisesMessage(SuspiciousOperation, msg % invalid_path):
+                    extract(os.path.join(archives_dir, entry), tmpdir)
diff --git a/tests/utils_tests/traversal_archives/traversal.tar b/tests/utils_tests/traversal_archives/traversal.tar
new file mode 100644
index 0000000000..07eede517a
--- /dev/null
+++ b/tests/utils_tests/traversal_archives/traversal.tar
diff --git a/tests/utils_tests/traversal_archives/traversal_absolute.tar b/tests/utils_tests/traversal_archives/traversal_absolute.tar
new file mode 100644
index 0000000000..231566b069
--- /dev/null
+++ b/tests/utils_tests/traversal_archives/traversal_absolute.tar
diff --git a/tests/utils_tests/traversal_archives/traversal_disk_win.tar b/tests/utils_tests/traversal_archives/traversal_disk_win.tar
new file mode 100644
index 0000000000..97f0b95501
--- /dev/null
+++ b/tests/utils_tests/traversal_archives/traversal_disk_win.tar
diff --git a/tests/utils_tests/traversal_archives/traversal_disk_win.zip b/tests/utils_tests/traversal_archives/traversal_disk_win.zip
new file mode 100644
index 0000000000..e5ab208398
--- /dev/null
+++ b/tests/utils_tests/traversal_archives/traversal_disk_win.zip