CVE-2026-6691 MongoDB Inc. CVE debrief

Who should care

Users of MongoDB C Driver, especially those using authMechanism=GSSAPI, should review and update their installations to prevent potential heap buffer overflow attacks. This includes administrators and developers responsible for MongoDB C Driver deployments, as well as security teams and vulnerability management teams. The vulnerability's impact on affected systems and potential operational disruptions should be assessed.

Technical summary

The MongoDB C Driver's Cyrus SASL integration is vulnerable to a heap buffer overflow due to unsafe string copying during username canonicalization. This issue can be triggered by passing untrusted input in the username of a MongoDB URI with authMechanism=GSSAPI. The vulnerability has a CVSS score of 8.6 and is classified as HIGH severity. Users of MongoDB C Driver, especially those using authMechanism=GSSAPI, should review and update their installations to prevent potential heap buffer overflow attacks. The issue requires updates to the MongoDB C Driver to address the vulnerability.

Defensive priority

High priority should be given to updating MongoDB C Driver installations, especially those using authMechanism=GSSAPI, to prevent potential heap buffer overflow attacks. This should be done in conjunction with reviewing and validating user input for MongoDB URIs and implementing additional security measures.

Recommended defensive actions

• Update MongoDB C Driver to version 2.1.2 or later
• Review and validate user input for MongoDB URIs with authMechanism=GSSAPI
• Implement additional security measures to monitor and restrict network traffic
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-05-06T16:16:11.483Z and was last modified on 2026-06-18T17:18:13.887Z. The NVD entry is currently Analyzed. Evidence from the CVE record and NVD entry indicates a heap buffer overflow vulnerability in the MongoDB C Driver's Cyrus SASL integration. The vulnerability is triggered by passing untrusted input in the username of a MongoDB URI with authMechanism=GSSAPI. The issue has a CVSS score of 8.6 and is classified as HIGH severity. Users should review and update their installations to prevent potential heap buffer overflow attacks.

Official resources