CVE-2026-84966: MongoDB C++ Driver

Medium severity, CVSS 5.5. EPSS: 0.1% chance of exploitation in the next 30 days.

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 products

• MongoDB C++ Driver: from 3.0.0, before 4.5.2 (fixed in 4.5.2)

Published 2026-09-03. Last modified 2026-09-22.