CVE-2026-84963 Silent field truncation via unchecked int cast of huge JSON string values in JSON-to-BSON parser

What is CVE-2026-84963?

CVE-2026-84963 is a medium-severity vulnerability in MongoDB C Driver, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

An incorrect numeric conversion in the JSON parsing component of the MongoDB C Driver's BSON library may cause an unusually large text value to be silently shortened, or the corresponding field to be omitted, while the parsing operation still reports success and returns no error. An unauthenticated party who can supply the input processed by an application that uses this component may cause that application to hold data that does not match what was submitted, which may result in unintended alteration of data.

Weakness: CWE-681

Which versions are affected by CVE-2026-84963?

It affects 1 product.

Products include Mongodb C Driver.

How do I fix CVE-2026-84963?

Upgrade to a fixed version.

Is CVE-2026-84963 being exploited?

There is no known exploitation of CVE-2026-84963 in the wild and no public exploit code.

Other vulnerabilities in MongoDB C Driver

• CVE-2026-93393 Heap overflow via oversized decrypted TLS record sequence in Windows Secure Channel stream Critical 9.2
• CVE-2026-6691 MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow High 8.6
• CVE-2026-84964 Heap corruption via OCSP request double free from crafted multi-URL certificate in TLS client High 8.2
• CVE-2024-7553 Accessing Untrusted Directory May Allow Local Privilege Escalation High 7.3
• CVE-2026-93395 Integer Underflow → Heap Out-of-Bounds Read in `bson_new_from_buffer() Medium 6.9

Sources

• CVE record
• NVD
• OSV
• How this page is made

Also known as DEBIAN-CVE-2026-84963, UBUNTU-CVE-2026-84963.