# CVE-2026-126792: libmongocrypt out-of-bounds write in key-management request builder

Source: https://junglewise.ai/threats/cve-2026-126792-a-memory-safety-flaw-in-the-key-management-request-building  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-13. Updated: 2026-11-13  
License: CC BY 4.0 with a link back

CVE-2026-126792 · Severity: medium · CVSS 4.7 · Published 2026-11-13

libmongocrypt, a cryptographic library used by MongoDB drivers and applications, contains a memory safety flaw in its key-management request-building component that can cause heap corruption. An attacker with high-privilege control over the in-process key-management provider configuration can trigger an out-of-bounds write, resulting in abnormal process termination and potential data corruption.

Technologies: [MongoDB Libmongocrypt](https://junglewise.ai/threats/technologies/libmongocrypt). Vendors: [MongoDB](https://junglewise.ai/threats/vendors/mongodb).

## Quick answers

**Is CVE-2026-126792 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126792 being exploited in the wild.

**How severe is CVE-2026-126792?** Medium severity, with a CVSS score of 4.7, published 13 November 2026.

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

**Is there a fix for CVE-2026-126792?** 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-2026-126792 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-126792?** Check whether you run MongoDB Libmongocrypt. 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 out-of-bounds heap write in libmongocrypt's key-management request builder, caused by use of a fixed-size output buffer without validation of the cryptographic key size supplied by a custom key-management callback. When an embedding application provides its own cryptographic callback implementation with oversized keys, data larger than the buffer is written past its end. Exploitation requires high-privilege access to configure the in-process key provider, and demonstrated impact is abnormal process termination due to memory corruption.

## Affected products

- MongoDB libmongocrypt

## Timeline

- 2026-11-13: disclosed

## References

- [https://jira.mongodb.org/browse/MONGOCRYPT-975](https://jira.mongodb.org/browse/MONGOCRYPT-975)
- [https://jira.mongodb.org/browse/PYTHON-5999](https://jira.mongodb.org/browse/PYTHON-5999)

## Related threats

- [libmongocrypt KMS request injection in key vault processing](https://junglewise.ai/threats/cve-2026-114655-libmongocrypt-builds-requests-to-external-key-management)
- [MongoDB libmongocrypt state management memory corruption](https://junglewise.ai/threats/cve-2026-106433-improper-state-management-in-mongodb-libmongocrypt-can-cause)
- [MongoDB Crypt key vault privilege escalation to Google Cloud KMS](https://junglewise.ai/threats/cve-2026-84962-mongodb-crypt-key-vault-privilege-escalation-to-google-cloud-kms)
- [MongoDB libmongocrypt denial of service via undersized encrypted payload](https://junglewise.ai/threats/cve-2026-84971-mongodb-libmongocrypt-denial-of-service-via-undersized-encrypted)
- [MongoDB libmongocrypt input validation bypass in automatic encryption](https://junglewise.ai/threats/cve-2026-81523-mongodb-libmongocrypt-input-validation-bypass-in-automatic)