# CVE-2026-96749: Heap out-of-bounds write via signed size overflow in BSON document encoding

> CVE-2026-96749: Heap out-of-bounds write via signed size overflow in BSON document encoding. CVSS 8.4 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-96749
Last updated: 2026-09-26T04:17:52Z

- Published: 2026-09-24 18:18 UTC · Updated: 2026-09-26 04:17 UTC · Assigner: mongodb
- CVSS: 8.4 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS: 0.19%, 8th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-190

## Description

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 vendors and products

- MongoDB: Python Driver

## Tracked companies

- [MongoDB Atlas](https://rewindex.com/company/mongodb-atlas.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-96749)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-96749)
- [https://github.com/mongodb/mongo-python-driver/blob/4.18.2/doc/changelog.rst](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://github.com/mongodb/mongo-python-driver/releases/tag/4.18.2)
- [https://github.com/mongodb/mongo-python-driver/security/advisories/GHSA-v4x9-3549-crwv](https://github.com/mongodb/mongo-python-driver/security/advisories/GHSA-v4x9-3549-crwv)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-96749 · Markdown: https://rewindex.com/cve/CVE-2026-96749.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-96749 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T04:04:36.311Z