CVE-2026-6691

Heap buffer overflow via unsafe username copying

Published May 6, 2026 · Updated May 6, 2026

Heap buffer overflow in MongoDB C Driver 2.1.0 through 2.1.2 allows local users to corrupt memory through a crafted GSSAPI username. The Cyrus SASL username canonicalization path copies the URI username into a heap buffer without checking that the destination is large enough. The flaw triggers before authentication or network traffic, but requires an application to accept an untrusted username in a MongoDB URI with authMechanism=GSSAPI.

CVSS severity8.6
High
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in MongoDB C Driver 2.1.0 through 2.1.2 allows local users to corrupt memory through a crafted GSSAPI username. The Cyrus SASL username canonicalization path copies the URI username into a heap buffer without checking that the destination is large enough. The flaw triggers before authentication or network traffic, but requires an application to accept an untrusted username in a MongoDB URI with authMechanism=GSSAPI.

The record

CVE
CVE-2026-6691
Published
May 6, 2026
Updated
May 6, 2026
Vendor
MongoDB
Product
MongoDB C++ Driver
Classifications
CWE-120, CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 6, 2026CVE publishedPublication date reported by the CVE source.
  2. May 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.1.0 <=2.1.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

MongoDB · MongoDB C++ Driverversion=2.1.0 <=2.1.2

Published CVSS scores

7.8MongoDB, Inc.CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.6MongoDB, Inc.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 describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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