CVE-2026-6691 PUBLISHED

MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow

Assigner: mongodb
Reserved: 20.04.2026 Published: 06.05.2026 Updated: 07.05.2026

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 Vector: CVSS: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 Score: 8.6

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Local	Confidentiality	High	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

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

Attack Vector	Local	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	High
Privileges Required	None	Integrity Impact	High
User Interaction	Required	Availability Impact	High

CVSS 3.1

Product Status

Vendor	MongoDB Inc.
Product	MongoDB C Driver
Versions	Default: unaffected affected from 2.1.0 to 2.1.2 (incl.)

References

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

Problem Types

CWE-120 Buffer Copy without Checking Size of Input CWE

Impacts

CAPEC-100 Overflow Buffers