Origin: upstream
Last-Update: 2013-09-03
Subject: directory traversal with ``ssi`` template tag

Django's template language includes two methods of including and
rendering one template inside another:

1. The ``{% include %}`` tag takes a template name, and uses Django's
   template loading mechanism (which is restricted to the directories
   specified in the ``TEMPLATE_DIRS`` setting, as with any other
   normal template load in Django).

2. The ``{% ssi %}`` tag, which takes a file path and includes that
   file's contents (optionally parsing and rendering it as a
   template).

Since the ``ssi`` tag is not restricted to ``TEMPLATE_DIRS``, it
represents a security risk; the setting ``ALLOWED_INCLUDE_ROOTS`` thus
is required, and specifies filesystem locations from which ``ssi`` may
read files.

To remedy this, the ``ssi`` tag will now use Python's
``os.path.abspath`` to determine the absolute path of the file, and
whether it is actually located within a directory permitted by
``ALLOWED_INCLUDE_ROOTS``.

--- a/django/template/defaulttags.py
+++ b/django/template/defaulttags.py
@@ -1,5 +1,6 @@
 """Default tags used by the template system, available to all templates."""
 
+import os
 import sys
 import re
 from datetime import datetime
@@ -309,6 +310,7 @@
         return ''
 
 def include_is_allowed(filepath):
+    filepath = os.path.abspath(filepath)
     for root in settings.ALLOWED_INCLUDE_ROOTS:
         if filepath.startswith(root):
             return True
--- a/tests/regressiontests/templates/tests.py
+++ b/tests/regressiontests/templates/tests.py
@@ -1764,3 +1764,34 @@
             template.Template('{% include "child" only %}').render(ctx),
             'none'
         )
+
+
+class SSITests(unittest.TestCase):
+    def setUp(self):
+        self.this_dir = os.path.dirname(os.path.abspath(__file__))
+        self.ssi_dir = os.path.join(self.this_dir, "templates", "first")
+
+    def render_ssi(self, path):
+        # the path must exist for the test to be reliable
+        self.assertTrue(os.path.exists(path))
+        return template.Template('{%% load ssi from future %%}{%% ssi "%s" %%}' % path).render(Context())
+
+    def test_allowed_paths(self):
+        acceptable_path = os.path.join(self.ssi_dir, "..", "first", "test.html")
+        with override_settings(ALLOWED_INCLUDE_ROOTS=(self.ssi_dir,)):
+            self.assertEqual(self.render_ssi(acceptable_path), 'First template\n')
+
+    def test_relative_include_exploit(self):
+        """
+        May not bypass ALLOWED_INCLUDE_ROOTS with relative paths
+
+        e.g. if ALLOWED_INCLUDE_ROOTS = ("/var/www",), it should not be
+        possible to do {% ssi "/var/www/../../etc/passwd" %}
+        """
+        disallowed_paths = [
+            os.path.join(self.ssi_dir, "..", "ssi_include.html"),
+            os.path.join(self.ssi_dir, "..", "second", "test.html"),
+        ]
+        with override_settings(ALLOWED_INCLUDE_ROOTS=(self.ssi_dir,)):
+            for path in disallowed_paths:
+                self.assertEqual(self.render_ssi(path), '')