CVE-2026-84970: 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.
Affected Software
Event History
Frequently Asked Questions
Which applications are exposed to this issue?
Applications that use the MongoDB C++ Driver BSON library and pass attacker-controlled JSON text to its public JSON parsing interface are exposed. The impact is limited to the local process using the library; a MongoDB server is not required.
What must an attacker provide to trigger the issue?
The attacker must be able to control JSON text supplied by the embedding application to the library's public parser. The input must be very large, and no credentials or user interaction are required.
Are default deployments affected?
Yes. The issue does not require a MongoDB server or any non-default configuration; exposure depends on whether the application parses sufficiently large attacker-controlled JSON input.
What are the possible effects on an affected process?
The parser may read memory beyond the supplied buffer and return that data to the caller, silently treat only part of the input as a complete document, or terminate the process.