Return 404 instead of IndexError for traversal past the root

CHANGES.rst

@@ -14,7 +14,10 @@ https://github.com/zopefoundation/Zope/blob/4.x/CHANGES.rst
 
 - Update to newest compatible versions of dependencies.
 
-- Added CC-BY 4.0 license to the Zope logo. 
+- Added CC-BY 4.0 license to the Zope logo.
+
+- Fix ``IndexError`` on traversal past the root using `..`.
+  (`#1218 <https://github.com/zopefoundation/Zope/issues/1218>`_)
 
 
 5.10 (2024-05-18)

src/ZPublisher/BaseRequest.py

@@ -366,6 +366,8 @@ def traverse(self, path, response=None, validated_hook=None):
             if not item or item == '.':
                 continue
             elif item == '..':
+                if not len(clean):
+                    return response.notFoundError(path)
                 del clean[-1]
             else:
                 clean.append(item)

src/ZPublisher/tests/testBaseRequest.py

@@ -373,6 +373,18 @@ def test_traverse_slash(self):
         self.assertEqual(r.URL, '/index_html')
         self.assertEqual(r.response.base, '')
 
+    def test_traverse_special_names(self):
+        root, folder = self._makeRootAndFolder()
+        r = self._makeOne(root)
+        self.assertRaises(NotFound, r.traverse, 'REQUEST')
+        self.assertRaises(NotFound, r.traverse, 'aq_self')
+        self.assertRaises(NotFound, r.traverse, 'aq_base')
+
+    def test_traverse_past_root(self):
+        root, folder = self._makeRootAndFolder()
+        r = self._makeOne(root)
+        self.assertRaises(NotFound, r.traverse, '..')
+
     def test_traverse_attribute_with_docstring(self, use_docstring=None):
         root, folder = self._makeRootAndFolder()
         folder._setObject('objBasic', self._makeBasicObject(use_docstring))