CVE-2026-84970 Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser
Attackers can trigger heap over-reads or crashes in applications using the MongoDB C++ Driver by supplying large JSON inputs due to integer truncation.
- 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-2026-84970?
CVE-2026-84970 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
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.
Weakness: CWE-681
Which versions are affected by CVE-2026-84970?
It affects 1 product.
Products include Mongodb C\+\+ Driver.
How do I fix CVE-2026-84970?
Apply the vendor's patch.
Is CVE-2026-84970 being exploited?
There is no known exploitation of CVE-2026-84970 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-2026-84966 BSON element injection via NUL-embedded document keys in builder append
Sources
Also known as DEBIAN-CVE-2026-84970, GHSA-j94p-2ppx-483m, UBUNTU-CVE-2026-84970.