High severity · published May 6, 2026
CVE-2026-6691
MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
7.8
CVSS
0.1%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.1% · higher than 2% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MC
MongoDB C Driver · MongoDB Inc.
2.1.0 through 2.1.2 · source: vendor
CD
C Driver · Mongodb
2.1.0 before 2.1.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6691
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6691
Patch
https://jira.mongodb.org/browse/CDRIVER-6134
More from MongoDB C Driver
3.7
CVE-2026-4359
Heap-buffer-over-read in _mongoc_http_send via strstr on non-null-terminated buffer