MongoDB C++ Driver BSON JSON Parse Truncation & Overread
CVE-2026-84970 Published on September 3, 2026

Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser
A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

NVD

Vulnerability Analysis

CVE-2026-84970 is exploitable with local system access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.

Attack Vector:
LOCAL
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE

Weakness Type

Incorrect Conversion between Numeric Types

When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.


Products Associated with CVE-2026-84970

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MongoDB C Driver
 

Affected Versions

MongoDB C++ Driver: