apply max_form_memory_size another level up in the parser

CHANGES.rst

@@ -1,3 +1,9 @@
+0.19.7
+------
+
+* Security Fix how ``max_form_memory_size`` is applied when parsing large
+  non-file fields. https://github.com/advisories/GHSA-q34m-jh98-gwm2
+
 0.19.6 2024-05-19
 -----------------
 

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "Quart"
-version = "0.19.6"
+version = "0.19.7.dev"
 description = "A Python ASGI web microframework with the same API as Flask"
 authors = ["pgjones <philip.graham.jones@googlemail.com>"]
 classifiers = [

src/quart/formparser.py

@@ -15,6 +15,7 @@
 from urllib.parse import parse_qsl
 
 from werkzeug.datastructures import Headers, MultiDict
+from werkzeug.exceptions import RequestEntityTooLarge
 from werkzeug.formparser import default_stream_factory
 from werkzeug.http import parse_options_header
 from werkzeug.sansio.multipart import Data, Epilogue, Field, File, MultipartDecoder, NeedData
@@ -173,19 +174,28 @@ async def parse(
         files = []
 
         current_part: Field | File
+        field_size: int | None = None
         async for data in body:
             parser.receive_data(data)
             event = parser.next_event()
             while not isinstance(event, (Epilogue, NeedData)):
                 if isinstance(event, Field):
                     current_part = event
+                    field_size = 0
                     container = []
                     _write = container.append
                 elif isinstance(event, File):
                     current_part = event
+                    field_size = None
                     container = self.start_file_streaming(event, content_length)
                     _write = container.write
                 elif isinstance(event, Data):
+                    if field_size is not None:
+                        field_size += len(event.data)
+
+                        if field_size > self.max_form_memory_size:
+                            raise RequestEntityTooLarge()
+
                     _write(event.data)
                     if not event.more_data:
                         if isinstance(current_part, Field):

tests/test_formparser.py

@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+import pytest
+from werkzeug.exceptions import RequestEntityTooLarge
+
+from quart.formparser import MultiPartParser
+from quart.wrappers.request import Body
+
+
+async def test_multipart_max_form_memory_size() -> None:
+    """max_form_memory_size is tracked across multiple data events."""
+    data = b"--bound\r\nContent-Disposition: form-field; name=a\r\n\r\n"
+    data += b"a" * 15 + b"\r\n--bound--"
+    body = Body(None, None)
+    body.set_result(data)
+    # The buffer size is less than the max size, so multiple data events will be
+    # returned. The field size is greater than the max.
+    parser = MultiPartParser(max_form_memory_size=10, buffer_size=5)
+
+    with pytest.raises(RequestEntityTooLarge):
+        await parser.parse(body, b"bound", 0)