PyMongo: PYTHON-5996 Heap out-of-bounds write via signed size overflow in BSON document encoding
An integer overflow in the BSON document encoding component of the MongoDB Python Driver's bundled native extension may occur when a single document is built from an unusually large amount of caller-supplied data. Size arithmetic is performed in a signed 32-bit type, and the guard meant to catch the overflow is written in a form whose behavior is not defined by the C language standard. A party with no privileges who can place a very large value into data that an application encodes may, depending on how the native extension was built, cause a write outside the bounds of an allocated buffer inside the application's own process.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pymongo | < 4.18.2 | 4.18.2 |
References
- https://github.com/mongodb/mongo-python-driver/security/advisories/GHSA-v4x9-3549-crwv
- https://nvd.nist.gov/vuln/detail/CVE-2026-96749
- https://github.com/mongodb/mongo-python-driver/pull/3066
- https://github.com/mongodb/mongo-python-driver/commit/640dd2383a1a2fb1a10e5222d50ebc0b22a61bd7
- https://github.com/mongodb/mongo-python-driver/commit/6ab44be0e97c9d1d5a23725c4978fb25f3249485
- https://github.com/mongodb/mongo-python-driver
- https://github.com/mongodb/mongo-python-driver/blob/4.18.2/doc/changelog.rst
- https://github.com/mongodb/mongo-python-driver/releases/tag/4.18.2
- https://www.mongodb.com/community/forums/t/pymongo-4-18-2-released/343732
- https://pypi.org/project/pymongo
- https://github.com/advisories/GHSA-v4x9-3549-crwv
- CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- Weakness (CWE)
CWE-190- Platform
- Python (PyPI)
- Package
pymongo- Disclosed
- 05.10.2026
- Updated
- 15.10.2026 18:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-4296 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-v4x9-3549-crwv - CC BY 4.0
Vulnerability history: pymongo
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 6
- First → latest
- 08.2013 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 4
Disclosures per year
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 0
- 2026: 4
earlier: 1
-
PyMongo: PYTHON-5996 Heap out-of-bounds write via signed size overflow in BSON document encoding this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.