# CVE-2026-93395: libbson integer underflow in BSON parsing

Source: https://junglewise.ai/threats/cve-2026-93395-libbson-integer-underflow-in-bson-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-17. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93395 · Severity: medium · CVSS 5.3 · Published 2026-09-17

libbson is a C library for parsing and generating BSON (Binary JSON) data, commonly used in MongoDB and other applications. A crafted BSON document with a zero-length prefix can trigger an integer underflow vulnerability that causes a heap out-of-bounds read, crashing applications that use the vulnerable API. This results in a denial of service for any service that accepts and processes BSON input.

Technologies: [MongoDB C Driver](https://junglewise.ai/threats/technologies/c-driver). Vendors: [MongoDB](https://junglewise.ai/threats/vendors/mongodb).

## Quick answers

**Is CVE-2026-93395 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93395 being exploited in the wild.

**How severe is CVE-2026-93395?** Medium severity, with a CVSS score of 5.3, published 17 September 2026.

**Which products and versions are affected?** MongoDB libbson.

**Is there a fix for CVE-2026-93395?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-93395 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-93395?** Check whether you run MongoDB C Driver or MongoDB Libbson. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is an integer underflow in the bson_new_from_buffer() function caused by missing lower-bound validation on the BSON document length field. The function reads a 32-bit length from the input buffer but does not verify that the value is at least 5 bytes (the minimum valid BSON document size). When the length is zero, an array index calculation wraps to UINT32_MAX, resulting in a heap out-of-bounds read. The attack vector is network-based if BSON input is accepted over the network, and requires no authentication. An attacker can trigger a denial of service by crashing the process with specially crafted BSON data. A patch validating the minimum document length would remediate this issue.

## Affected products

- MongoDB libbson

## Timeline

- 2026-09-17: disclosed

## References

- [https://jira.mongodb.org/browse/CDRIVER-6343](https://jira.mongodb.org/browse/CDRIVER-6343)

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