From 5a56cdcbaec2153cd67596c6c2c8056e1ea5ed56 Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Tue, 2 May 2023 11:31:10 +0000
Subject: [PATCH] Merge pull request from GHSA-xg9f-g7g7-2323

limit the maximum number of multipart form parts

CVE: CVE-2023-25577

Upstream-Status: Backport [https://github.com/pallets/werkzeug/commit/517cac5a804e8c4dc4ed038bb20dacd038e7a9f1]

Signed-off-by: Narpat Mali <narpat.mali@windriver.com>
---
 CHANGES.rst                      |  5 +++++
 docs/request_data.rst            | 37 +++++++++++++++++---------------
 src/werkzeug/formparser.py       | 12 ++++++++++-
 src/werkzeug/sansio/multipart.py |  8 +++++++
 src/werkzeug/wrappers/request.py |  8 +++++++
 tests/test_formparser.py         |  9 ++++++++
 6 files changed, 61 insertions(+), 18 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index a351d7c..6e809ba 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,5 +1,10 @@
 .. currentmodule:: werkzeug

+-   Specify a maximum number of multipart parts, default 1000, after which a
+    ``RequestEntityTooLarge`` exception is raised on parsing. This mitigates a DoS
+    attack where a larger number of form/file parts would result in disproportionate
+    resource use.
+
 Version 2.1.1
 -------------

diff --git a/docs/request_data.rst b/docs/request_data.rst
index 83c6278..e55841e 100644
--- a/docs/request_data.rst
+++ b/docs/request_data.rst
@@ -73,23 +73,26 @@ read the stream *or* call :meth:`~Request.get_data`.
 Limiting Request Data
 ---------------------

-To avoid being the victim of a DDOS attack you can set the maximum
-accepted content length and request field sizes.  The :class:`Request`
-class has two attributes for that: :attr:`~Request.max_content_length`
-and :attr:`~Request.max_form_memory_size`.
-
-The first one can be used to limit the total content length.  For example
-by setting it to ``1024 * 1024 * 16`` the request won't accept more than
-16MB of transmitted data.
-
-Because certain data can't be moved to the hard disk (regular post data)
-whereas temporary files can, there is a second limit you can set.  The
-:attr:`~Request.max_form_memory_size` limits the size of `POST`
-transmitted form data.  By setting it to ``1024 * 1024 * 2`` you can make
-sure that all in memory-stored fields are not more than 2MB in size.
-
-This however does *not* affect in-memory stored files if the
-`stream_factory` used returns a in-memory file.
+The :class:`Request` class provides a few attributes to control how much data is
+processed from the request body. This can help mitigate DoS attacks that craft the
+request in such a way that the server uses too many resources to handle it. Each of
+these limits will raise a :exc:`~werkzeug.exceptions.RequestEntityTooLarge` if they are
+exceeded.
+
+-   :attr:`~Request.max_content_length` Stop reading request data after this number
+    of bytes. It's better to configure this in the WSGI server or HTTP server, rather
+    than the WSGI application.
+-   :attr:`~Request.max_form_memory_size` Stop reading request data if any form part is
+    larger than this number of bytes. While file parts can be moved to disk, regular
+    form field data is stored in memory only.
+-   :attr:`~Request.max_form_parts` Stop reading request data if more than this number
+    of parts are sent in multipart form data. This is useful to stop a very large number
+    of very small parts, especially file parts. The default is 1000.
+
+Using Werkzeug to set these limits is only one layer of protection. WSGI servers
+and HTTPS servers should set their own limits on size and timeouts. The operating system
+or container manager should set limits on memory and processing time for server
+processes.


 How to extend Parsing?
diff --git a/src/werkzeug/formparser.py b/src/werkzeug/formparser.py
index 10d58ca..bebb2fc 100644
--- a/src/werkzeug/formparser.py
+++ b/src/werkzeug/formparser.py
@@ -179,6 +179,8 @@ class FormDataParser:
     :param cls: an optional dict class to use.  If this is not specified
                        or `None` the default :class:`MultiDict` is used.
     :param silent: If set to False parsing errors will not be caught.
+    :param max_form_parts: The maximum number of parts to be parsed. If this is
+        exceeded, a :exc:`~exceptions.RequestEntityTooLarge` exception is raised.
     """

     def __init__(
@@ -190,6 +192,8 @@ class FormDataParser:
         max_content_length: t.Optional[int] = None,
         cls: t.Optional[t.Type[MultiDict]] = None,
         silent: bool = True,
+        *,
+        max_form_parts: t.Optional[int] = None,
     ) -> None:
         if stream_factory is None:
             stream_factory = default_stream_factory
@@ -199,6 +203,7 @@ class FormDataParser:
         self.errors = errors
         self.max_form_memory_size = max_form_memory_size
         self.max_content_length = max_content_length
+        self.max_form_parts = max_form_parts

         if cls is None:
             cls = MultiDict
@@ -281,6 +286,7 @@ class FormDataParser:
             self.errors,
             max_form_memory_size=self.max_form_memory_size,
             cls=self.cls,
+            max_form_parts=self.max_form_parts,
         )
         boundary = options.get("boundary", "").encode("ascii")

@@ -346,10 +352,12 @@ class MultiPartParser:
         max_form_memory_size: t.Optional[int] = None,
         cls: t.Optional[t.Type[MultiDict]] = None,
         buffer_size: int = 64 * 1024,
+        max_form_parts: t.Optional[int] = None,
     ) -> None:
         self.charset = charset
         self.errors = errors
         self.max_form_memory_size = max_form_memory_size
+        self.max_form_parts = max_form_parts

         if stream_factory is None:
             stream_factory = default_stream_factory
@@ -409,7 +417,9 @@ class MultiPartParser:
             [None],
         )

-        parser = MultipartDecoder(boundary, self.max_form_memory_size)
+        parser = MultipartDecoder(
+            boundary, self.max_form_memory_size, max_parts=self.max_form_parts
+        )

         fields = []
         files = []
diff --git a/src/werkzeug/sansio/multipart.py b/src/werkzeug/sansio/multipart.py
index 2d54422..e7d742b 100644
--- a/src/werkzeug/sansio/multipart.py
+++ b/src/werkzeug/sansio/multipart.py
@@ -83,10 +83,13 @@ class MultipartDecoder:
         self,
         boundary: bytes,
         max_form_memory_size: Optional[int] = None,
+        *,
+        max_parts: Optional[int] = None,
     ) -> None:
         self.buffer = bytearray()
         self.complete = False
         self.max_form_memory_size = max_form_memory_size
+        self.max_parts = max_parts
         self.state = State.PREAMBLE
         self.boundary = boundary

@@ -113,6 +116,7 @@ class MultipartDecoder:
             % (LINE_BREAK, re.escape(boundary), LINE_BREAK, LINE_BREAK),
             re.MULTILINE,
         )
+        self._parts_decoded = 0

     def last_newline(self) -> int:
         try:
@@ -177,6 +181,10 @@ class MultipartDecoder:
                         name=name,
                     )
                 self.state = State.DATA
+                self._parts_decoded += 1
+
+                if self.max_parts is not None and self._parts_decoded > self.max_parts:
+                    raise RequestEntityTooLarge()

         elif self.state == State.DATA:
             if self.buffer.find(b"--" + self.boundary) == -1:
diff --git a/src/werkzeug/wrappers/request.py b/src/werkzeug/wrappers/request.py
index 57b739c..a6d5429 100644
--- a/src/werkzeug/wrappers/request.py
+++ b/src/werkzeug/wrappers/request.py
@@ -83,6 +83,13 @@ class Request(_SansIORequest):
     #: .. versionadded:: 0.5
     max_form_memory_size: t.Optional[int] = None

+    #: The maximum number of multipart parts to parse, passed to
+    #: :attr:`form_data_parser_class`. Parsing form data with more than this
+    #: many parts will raise :exc:`~.RequestEntityTooLarge`.
+    #:
+    #: .. versionadded:: 2.2.3
+    max_form_parts = 1000
+
     #: The form data parser that should be used.  Can be replaced to customize
     #: the form date parsing.
     form_data_parser_class: t.Type[FormDataParser] = FormDataParser
@@ -246,6 +253,7 @@ class Request(_SansIORequest):
             self.max_form_memory_size,
             self.max_content_length,
             self.parameter_storage_class,
+            max_form_parts=self.max_form_parts,
         )

     def _load_form_data(self) -> None:
diff --git a/tests/test_formparser.py b/tests/test_formparser.py
index 5fc803e..834324f 100644
--- a/tests/test_formparser.py
+++ b/tests/test_formparser.py
@@ -127,6 +127,15 @@ class TestFormParser:
         req.max_form_memory_size = 400
         assert req.form["foo"] == "Hello World"

+        req = Request.from_values(
+            input_stream=io.BytesIO(data),
+            content_length=len(data),
+            content_type="multipart/form-data; boundary=foo",
+            method="POST",
+        )
+        req.max_form_parts = 1
+        pytest.raises(RequestEntityTooLarge, lambda: req.form["foo"])
+
     def test_missing_multipart_boundary(self):
         data = (
             b"--foo\r\nContent-Disposition: form-field; name=foo\r\n\r\n"
--
2.40.0
