# CVE-2026-93395: Integer Underflow → Heap Out-of-Bounds Read in `bson_new_from_buffer()

> An integer underflow in libbson allows attackers to cause a denial of service via crafted BSON input.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-93395, GHSA-jm9m-v7jc-m4j8, UBUNTU-CVE-2026-93395

## What is CVE-2026-93395?

CVE-2026-93395 is a medium-severity vulnerability in MongoDB Inc. C Driver, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A missing lower-bound validation in the bson_new_from_buffer() function of libbson allows an integer underflow when processing BSON data with a zero-length prefix. The function reads a 32-bit document length from the input buffer but does not verify that the value is at least 5 (the minimum valid BSON document size) before using it in an array index calculation. When the length field is zero, the expression used to check the document's null terminator wraps to UINT32_MAX, causing a heap out-of-bounds read that crashes the process. An unauthorized party who can supply crafted BSON input to an application using this API can cause a denial of service.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-93395?

It affects 1 product.


Products: Mongodb C Driver.

## How do I fix CVE-2026-93395?

Apply the vendor's patch.

## Is CVE-2026-93395 being exploited?

There is no known exploitation of CVE-2026-93395 in the wild and no public exploit code.

## Other vulnerabilities in MongoDB Inc. 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-2025-12119](https://insights.sbomify.com/CVE-2025-12119/): Bulk write with options may read invalid memory (medium 6.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93395 and fix it if it is affected.

What it is: CVE-2026-93395 is a medium-severity vulnerability in MongoDB Inc. C Driver, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-93395 in the wild and no public exploit code.

Affected product: MongoDB Inc. 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-2026-93395/ (Markdown: https://insights.sbomify.com/CVE-2026-93395/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93395
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93395
- OSV: https://osv.dev/vulnerability/CVE-2026-93395

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93395/
Summaries are generated and may contain mistakes; the official description above is the record.