From 8760275afb72bd10b57d92cb4d52abf759b2f3a7 Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Fri, 25 Oct 2024 06:46:50 -0700
Subject: [PATCH] apply max_form_memory_size another level up in the parser

CVE: CVE-2024-49767

Upstream-Status: Backport [https://github.com/pallets/werkzeug/commit/8760275afb72bd10b57d92cb4d52abf759b2f3a7]

Signed-off-by: Soumya Sambu <soumya.sambu@windriver.com>
---
 src/werkzeug/formparser.py       | 11 +++++++++++
 src/werkzeug/sansio/multipart.py |  2 ++
 tests/test_formparser.py         | 12 ++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/src/werkzeug/formparser.py b/src/werkzeug/formparser.py
index bebb2fc..b82af82 100644
--- a/src/werkzeug/formparser.py
+++ b/src/werkzeug/formparser.py
@@ -405,6 +405,7 @@ class MultiPartParser:
     def parse(
         self, stream: t.IO[bytes], boundary: bytes, content_length: t.Optional[int]
     ) -> t.Tuple[MultiDict, MultiDict]:
+        field_size: int | None = None
         container: t.Union[t.IO[bytes], t.List[bytes]]
         _write: t.Callable[[bytes], t.Any]

@@ -431,13 +432,23 @@ class MultiPartParser:
             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 self.max_form_memory_size is not None and field_size is not None:
+                        # Ensure that accumulated data events do not exceed limit.
+                        # Also checked within single event in MultipartDecoder.
+                        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):
diff --git a/src/werkzeug/sansio/multipart.py b/src/werkzeug/sansio/multipart.py
index e7d742b..a91fedd 100644
--- a/src/werkzeug/sansio/multipart.py
+++ b/src/werkzeug/sansio/multipart.py
@@ -137,6 +137,8 @@ class MultipartDecoder:
             self.max_form_memory_size is not None
             and len(self.buffer) + len(data) > self.max_form_memory_size
         ):
+            # Ensure that data within single event does not exceed limit.
+            # Also checked across accumulated events in MultiPartParser.
             raise RequestEntityTooLarge()
         else:
             self.buffer.extend(data)
diff --git a/tests/test_formparser.py b/tests/test_formparser.py
index 834324f..1a178dd 100644
--- a/tests/test_formparser.py
+++ b/tests/test_formparser.py
@@ -459,3 +459,15 @@ class TestMultiPartParser:
         )
         assert request.files["rfc2231"].filename == "a b c d e f.txt"
         assert request.files["rfc2231"].read() == b"file contents"
+
+
+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--"
+    # 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 = formparser.MultiPartParser(max_form_memory_size=10, buffer_size=5)
+
+    with pytest.raises(RequestEntityTooLarge):
+        parser.parse(io.BytesIO(data), b"bound", None)
--
2.40.0
