# CVE-2026-84965: Heap write primitive via size round-up wrap during JSON parsing on 32-bit builds

> An integer overflow in the MongoDB C Driver's JSON parser on 32-bit systems allows unauthenticated attackers to cause a denial of service via large inputs.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-84965, UBUNTU-CVE-2026-84965

## What is CVE-2026-84965?

CVE-2026-84965 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 integer wraparound in an allocation size calculation in the BSON library's JSON parsing code can cause a buffer to be released while a following copy operation still writes through the stale pointer. On builds where sizes are 32 bits, an unauthenticated party able to supply a sufficiently large JSON input to an application that links the library may cause that application to terminate unexpectedly, resulting in denial of service.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-84965?

It affects 1 product.


Products: Mongodb C Driver.

## How do I fix CVE-2026-84965?

Upgrade to a fixed version.

## Is CVE-2026-84965 being exploited?

There is no known exploitation of CVE-2026-84965 in the wild and no public exploit code.

## Other vulnerabilities in MongoDB C Driver

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

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84965 and fix it if it is affected.

What it is: CVE-2026-84965 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.
Exploitation: There is no known exploitation of CVE-2026-84965 in the wild and no public exploit code.

Affected product: MongoDB C Driver. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84965/ (Markdown: https://insights.sbomify.com/CVE-2026-84965/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84965
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84965
- OSV: https://osv.dev/vulnerability/CVE-2026-84965

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84965/
Summaries are generated and may contain mistakes; the official description above is the record.