CVE-2026-84970: CWE-681: Incorrect Conversion between Numeric Types in MongoDB C++ Driver
Description
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.
CVSS v4.0
Score 5.9medium
Affected software
MongoDB
C++ Driver
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability involves incorrect conversion between numeric types (CWE-681) in the MongoDB C++ Driver's BSON library JSON parser. Specifically, when processing very large JSON input controlled by an attacker, the library can read out-of-bounds memory, return unintended data, truncate the input silently, or crash the process. The flaw is confined to the embedding application's process and does not impact MongoDB servers or require authentication. The affected version is exactly 3.2.0 of the MongoDB C++ Driver. No official remediation or patch has been documented at this time.
Potential Impact
An attacker able to supply large JSON input to the vulnerable parsing interface can cause memory disclosure (reading beyond buffer), silent data truncation, or denial of service via process termination. The impact is limited to the local process using the vulnerable library; no server compromise or credential access is involved.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid processing untrusted or very large JSON inputs with the affected MongoDB C++ Driver version 3.2.0.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mongodb
- Date Reserved
- 2026-09-02T17:58:52.743Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a998d5bacd9273b4916fcac
Added to database: 09/03/2026, 15:08:11 UTC
Last enriched: 09/07/2026, 13:06:22 UTC
Last updated: 10/19/2026, 06:48:20 UTC
Views: 68
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