---
id: CVE-2026-84966
title: >-
  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
summary: >-
  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 …
severity: medium
cvss: 5.1
cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-681
vendor: mongodb
product: c++_driver
affected:
  - 'c++_driver >= 3.0.0, < 4.5.2'
patched:
  - c++_driver 4.5.2
published: '2026-09-03'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T15:54:16.740'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84966'
references:
  - url: 'https://jira.mongodb.org/browse/CXX-3548'
    label: cna@mongodb.com
tags:
  - nvd
epss: 0.00142
epssPercentile: 0.02935
ingestedAt: '2026-09-22T16:06:00.459Z'
---

## Overview

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

- `c++_driver >= 3.0.0, < 4.5.2`

## Remediation

Upgrade past the affected range:

- `c++_driver 4.5.2`