From dee2cf1d1d87fbd480818c6bd7b9711e120a05b8 Mon Sep 17 00:00:00 2001
From: Madan Kumar <winklemad@outlook.com>
Date: Sun, 26 Jul 2026 05:41:57 +0530
Subject: [PATCH] PYTHON-XXXX Reject extra fields in JSON timestamps

---
 bson/json_util.py      |  2 ++
 doc/changelog.rst      |  2 ++
 doc/contributors.rst   |  1 +
 test/test_json_util.py | 12 ++++++++++++
 4 files changed, 17 insertions(+)

diff --git a/bson/json_util.py b/bson/json_util.py
index 098a4b18ce..f01cd6cd19 100644
--- a/bson/json_util.py
+++ b/bson/json_util.py
@@ -789,6 +789,8 @@ def _parse_binary(doc: Any, json_options: JSONOptions) -> Union[Binary, uuid.UUI
 
 def _parse_timestamp(doc: Any, dummy0: Any) -> Timestamp:
     tsp = doc["$timestamp"]
+    if set(tsp) != {"t", "i"}:
+        raise TypeError(f'$timestamp must include exactly "t" and "i" components: {doc}')
     return Timestamp(tsp["t"], tsp["i"])
 
 
diff --git a/doc/changelog.rst b/doc/changelog.rst
index c272714376..cda288c575 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -25,6 +25,8 @@ PyMongo 4.18 brings a number of changes including:
   the bytes remaining in the array now raises
   :class:`~bson.errors.InvalidBSON` instead of reading past the end of the
   buffer.
+- Fixed :func:`bson.json_util.loads` to reject ``$timestamp`` values containing
+  fields other than ``t`` and ``i``.
 
 Changes in Version 4.17.0 (2026/04/20)
 --------------------------------------
diff --git a/doc/contributors.rst b/doc/contributors.rst
index d36731159e..6c2cff68a3 100644
--- a/doc/contributors.rst
+++ b/doc/contributors.rst
@@ -109,3 +109,4 @@ The following is a list of people who have contributed to
 - Noah Stapp (NoahStapp)
 - Cal Jacobson (cj81499)
 - Sophia Yang (sophiayangDB)
+- Madan Kumar (winklemad)
diff --git a/test/test_json_util.py b/test/test_json_util.py
index cd86456ab0..f1b781d3d9 100644
--- a/test/test_json_util.py
+++ b/test/test_json_util.py
@@ -405,6 +405,18 @@ def test_timestamp(self):
         self.assertEqual(dct, rtdct)
         self.assertEqual('{"ts": {"$timestamp": {"t": 4, "i": 13}}}', res)
 
+    def test_timestamp_with_invalid_fields(self):
+        invalid_values = [
+            '{"t": 4, "i": 13, "extra": 1}',
+            '{"t": 4, "unexpected": 13}',
+        ]
+        for value in invalid_values:
+            with self.subTest(value=value):
+                with self.assertRaisesRegex(
+                    TypeError, r'\$timestamp must include exactly "t" and "i" components'
+                ):
+                    json_util.loads(f'{{"ts": {{"$timestamp": {value}}}}}')
+
     def test_uuid_default(self):
         # Cannot directly encode native UUIDs with the default
         # uuid_representation.