CVE-2026-84966 BSON element injection via NUL-embedded document keys in builder append
An integer overflow in the MongoDB C++ Driver allows attackers to cause a denial of service via oversized field names.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84966?
CVE-2026-84966 is a medium-severity vulnerability in MongoDB C++ Driver, published on 3 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-681
Which versions are affected by CVE-2026-84966?
It affects 1 product.
Products include Mongodb C\+\+ Driver.
How do I fix CVE-2026-84966?
Upgrade to a fixed version.
Is CVE-2026-84966 being exploited?
There is no known exploitation of CVE-2026-84966 in the wild and no public exploit code.
Other vulnerabilities in MongoDB C++ Driver
- CVE-2026-81522 Cross-tenant database retargeting via dot/NUL injection in namespace strings in the C++ Driver
- CVE-2026-88034 GridFS data disclosure and deletion via query-operator injection in file IDs in the MongoDB C++ Driver
- CVE-2026-84970 Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser
Sources
Also known as DEBIAN-CVE-2026-84966, UBUNTU-CVE-2026-84966.