Prevent reflected file downloads on specially-named files

This fixes #196, where it was observed that django_downloadview
was vulnerable to reflected file download attacks with
specially-named files, similar to CVE-2022-36359 in Django.
This change adopts the same replacement rules as used in Django's fix
in commit b3e4494d759202a3b6bf247fd34455bf13be5b80.

django_downloadview/response.py

@@ -72,9 +72,16 @@ def content_disposition(filename):
     """
     if not filename:
         return "attachment"
-    ascii_filename = encode_basename_ascii(filename)
+    # ASCII filenames are quoted and must ensure escape sequences
+    # in the filename won't break out of the quoted header value
+    # which can permit a reflected file download attack. The UTF-8
+    # version is immune because it's not quoted.
+    ascii_filename = (
+        encode_basename_ascii(filename).replace("\\", "\\\\").replace('"', r'\"')
+    )
     utf8_filename = encode_basename_utf8(filename)
     if ascii_filename == utf8_filename:  # ASCII only.
+
         return f'attachment; filename="{ascii_filename}"'
     else:
         return (

tests/response.py

@@ -19,3 +19,16 @@ class DownloadResponseTestCase(unittest.TestCase):
         self.assertIn(
             "filename*=UTF-8''espac%C3%A9%20.txt", headers["Content-Disposition"]
         )
+
+    def test_content_disposition_escaping(self):
+        """Content-Disposition headers escape special characters."""
+        response = DownloadResponse(
+            "fake file",
+            attachment=True,
+            basename=r'"malicious\file.exe'
+        )
+        headers = response.default_headers
+        self.assertIn(
+            r'filename="\"malicious\\file.exe"',
+            headers["Content-Disposition"]
+        )