# CVE-2026-6691: MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow

> CVE-2026-6691: MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow. CVSS 7.8 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-6691
Last updated: 2026-06-18T17:18:13Z

- Published: 2026-05-06 15:08 UTC · Updated: 2026-06-18 17:18 UTC · Assigner: mongodb
- CVSS: 7.8 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS: 0.13%, 2th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-120

## Description

The MongoDB C Driver's Cyrus SASL integration performs unsafe string copying during username canonicalization, enabling a heap buffer overflow before any authentication or network traffic. This may be triggered by passing untrusted input in the username of a MongoDB URI with authMechanism=GSSAPI.

## Affected vendors and products

- MongoDB Inc.: MongoDB C Driver

## Tracked companies

- [MongoDB Atlas](https://rewindex.com/company/mongodb-atlas.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-6691)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-6691)
- [https://jira.mongodb.org/browse/CDRIVER-6134](https://jira.mongodb.org/browse/CDRIVER-6134)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-6691 · Markdown: https://rewindex.com/cve/CVE-2026-6691.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-6691 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:09:05.922Z