How severe is CVE-2026-6691?

CVE-2026-6691 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-6691 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6691?

CVE-2026-6691 affects Mongodb C Driver. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6691?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-6691 have an EU (EUVD) identifier?

Yes. CVE-2026-6691 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-27838.

When was CVE-2026-6691 published?

CVE-2026-6691 was published on 2026-05-06 and last updated on 2026-06-18.

CVE-2026-6691

CVE-2026-6691 is a high-severity vulnerability in Mongodb C Driver with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: High (CVSS 3.x base score 7.8)
CVSS v4: 8.6
EPSS exploit prediction: 0% (7th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-27838
Weakness: CWE-787
Affected product: Mongodb C Driver
Published: 2026-05-06
Last modified: 2026-06-18

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.

Frequently asked questions

What is CVE-2026-6691?: 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.
How severe is CVE-2026-6691?: CVE-2026-6691 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-6691 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-6691?: CVE-2026-6691 affects Mongodb C Driver. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-6691?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-6691 have an EU (EUVD) identifier?: Yes. CVE-2026-6691 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-27838.
When was CVE-2026-6691 published?: CVE-2026-6691 was published on 2026-05-06 and last updated on 2026-06-18.

References

https://jira.mongodb.org/browse/CDRIVER-6134

Affected products (1)

cpe:2.3:a:mongodb:c_driver:*:*:*:*:*:mongodb:*:*

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