CVE-2026-6691
CVE-2026-6691 is a high-severity vulnerability in Mongodb C Driver with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.
Key facts
- Severity: High (CVSS 3.x base score 7.8)
- CVSS v4: 8.6
- EPSS exploit prediction: 0% (3rd percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-27838
- Weakness: CWE-787
- Affected product: Mongodb C Driver
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-6691?
- 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.
- How severe is CVE-2026-6691?
- CVE-2026-6691 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
- Is CVE-2026-6691 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (3rd percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-6691?
- CVE-2026-6691 affects Mongodb C Driver. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-6691?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2026-6691 have an EU (EUVD) identifier?
- Yes. CVE-2026-6691 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-27838.
- When was CVE-2026-6691 published?
- CVE-2026-6691 was published on 2026-05-06 and last updated on 2026-06-18.
References
Affected products (1)
- cpe:2.3:a:mongodb:c_driver:*:*:*:*:*:mongodb:*:*
More vulnerabilities in Mongodb C Driver
- CVE-2024-7553 — High (CVSS 7.3): Incorrect validation of files loaded from a local untrusted directory may allow local privilege escalation if the…
- CVE-2025-12119 — Medium (CVSS 6.8): A mongoc_bulk_operation_t may read invalid memory if large options are passed.
- CVE-2020-12135 — Medium (CVSS 5.5): bson before 0.8 incorrectly uses int rather than size_t for many variables, parameters, and return values. In…
- CVE-2023-0437 — Medium (CVSS 5.3): When calling bson_utf8_validate on some inputs a loop with an exit condition that cannot be reached may occur, i.e. an…
- CVE-2026-6231 — Medium (CVSS 4.3): The bson_validate function may return early on specific inputs and incorrectly report success. This behavior could…
- CVE-2021-32050 — Medium (CVSS 4.2): Some MongoDB Drivers may erroneously publish events containing authentication-related data to a command listener…
All CVEs affecting Mongodb C Driver →
Other CWE-787 (Out-of-bounds Write) vulnerabilities
- CVE-2026-42369 — Critical (CVSS 10.0): GV-VMS V20 is a Video Monitoring Software used to gather the feeds of many surveillance cameras and manage other…
- CVE-2026-4746 — Critical (CVSS 10.0): Out-of-bounds Write vulnerability in timeplus-io proton (base/poco/Foundation/src modules). This vulnerability is…
- CVE-2025-43300 — Critical (CVSS 10.0): An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in iOS 15.8.5 and iPadOS…
- CVE-2025-24201 — Critical (CVSS 10.0): An out-of-bounds write issue was addressed with improved checks to prevent unauthorized actions. This issue is fixed in…
- CVE-2024-42479 — Critical (CVSS 10.0): llama.cpp provides LLM inference in C/C++. The unsafe `data` pointer member in the `rpc_tensor` structure can cause…
- CVE-2024-39791 — Critical (CVSS 10.0): Stack-based buffer overflow vulnerabilities affecting Vonets industrial wifi bridge relays and wifi bridge…