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.

CVSS 4.0

8.6CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS 3.1

7.8CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS

0.1% chance of exploitation in the next 30 days; higher than 2% of CVEs (scores of 2026-10-26)

CWEs

CWE-787, CWE-120

Published

2026-05-06

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Affected

• mongodb:c_driver

References

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

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