CVE-2026-6691
MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
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.
INFO
Published Date :
May 6, 2026, 4:16 p.m.
Last Modified :
June 18, 2026, 5:18 p.m.
Remotely Exploit :
No
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | HIGH | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update the MongoDB C Driver to a patched version.
- Avoid untrusted input in usernames with GSSAPI.
- Recompile applications using the driver.
Public PoC/Exploit Available at Github
CVE-2026-6691 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-6691.
| URL | Resource |
|---|---|
| https://jira.mongodb.org/browse/CDRIVER-6134 | Patch Vendor Advisory Issue Tracking |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-6691 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-6691
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Application Security Researcher | Secure Code Review | Vulnerability Research
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-6691 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-6691 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jun. 18, 2026
Action Type Old Value New Value Added CWE CWE-787 Added CPE Configuration OR *cpe:2.3:a:mongodb:c_driver:*:*:*:*:*:mongodb:*:* versions from (including) 2.1.0 up to (excluding) 2.1.2 Added Reference Type MongoDB, Inc.: https://jira.mongodb.org/browse/CDRIVER-6134 Types: Issue Tracking, Patch, Vendor Advisory -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'MongoDB Inc.', 'product': 'MongoDB C Driver', 'versions': [{'status': 'affected', 'version': '2.1.0', 'versionType': 'semver', 'lessThanOrEqual': '2.1.2'}], 'defaultStatus': 'unaffected'}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-6691', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-05-06T00:00:00+00:00'} -
New CVE Received by [email protected]
May. 06, 2026
Action Type Old Value New Value Added 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. Added CVSS V4.0 AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CVSS V3.1 AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Added CWE CWE-120 Added Reference https://jira.mongodb.org/browse/CDRIVER-6134