# CVE-2026-84966: BSON element injection via NUL-embedded document keys in builder append

> CVE-2026-84966: BSON element injection via NUL-embedded document keys in builder append. CVSS 5.1 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-84966
Last updated: 2026-09-22T15:54:16Z

- Published: 2026-09-03 15:00 UTC · Updated: 2026-09-22 15:54 UTC · Assigner: mongodb
- CVSS: 5.1 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS: 0.14%, 4th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-681

## Description

An incorrect numeric type conversion in the BSON document building component of the MongoDB C++ Driver may cause a length value to be interpreted incorrectly. When an application supplies an extremely large, non-terminated field name to the builder, the library may read memory outside the intended buffer and terminate the calling process. No authentication is required, but the calling application must pass the oversized name in a specific form.

## Affected vendors and products

- MongoDB: C++ 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-2026-84966)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-84966)
- [https://jira.mongodb.org/browse/CXX-3548](https://jira.mongodb.org/browse/CXX-3548)

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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-2026-84966 · Markdown: https://rewindex.com/cve/CVE-2026-84966.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-84966 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:13:08.310Z