CVE-2026-6691
MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
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.
Attack profile
How easy it is to exploit
- Attack vector
- Local
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
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.
- Record
CVE-2026-6691- CVSS 4.0
- 8.6 High
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 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-120
- Updated
- 2026-11-02
EUVDEUVD-2026-27838
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.
- Record
EUVD-2026-27838- CVSS 4.0
- 8.6 High
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 - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-587q-94wg-2pfp
The MongoDB C Driver's Cyrus SASL integration performs unsafe string copying during username...
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.
- Record
GHSA-587q-94wg-2pfp- CVSS 4.0
- 8.6 High
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/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 - CVSS 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-120, CWE-787
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2026-6691- CVSS 4.0
- 8.6 High
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/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 - CVSS 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-120, CWE-787
- Updated
- 2026-11-02
OSV
MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
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.
- Record
CVE-2026-6691- CVSS 4.0
- 8.6 High
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 - Weakness
- CWE-120
- Updated
- 2026-11-02
OSVDEBIAN-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.
- Record
DEBIAN-CVE-2026-6691- CVSS 4.0
- 8.6 High
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/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 - Updated
- 2026-11-02
Show 5 moreShow less
OSVOESA-2026-2690
mongo-c-driver security update
mongo-c-driver is a project that includes two libraries: libmongoc, a client library written in C for MongoDB. libbson, a library providing useful routines related to building, parsing, and iterating BSON documents.
Security Fix(es):
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.(CVE-2026-6691)
- Record
OESA-2026-2690- CVSS 4.0
- 8.6 High
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/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 - Updated
- 2026-11-02
OSVOESA-2026-2691
mongo-c-driver security update
mongo-c-driver is a project that includes two libraries: libmongoc, a client library written in C for MongoDB. libbson, a library providing useful routines related to building, parsing, and iterating BSON documents.
Security Fix(es):
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.(CVE-2026-6691)
- Record
OESA-2026-2691- CVSS 4.0
- 8.6 High
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/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 - Updated
- 2026-11-02
OSVOESA-2026-2692
mongo-c-driver security update
mongo-c-driver is a project that includes two libraries: libmongoc, a client library written in C for MongoDB. libbson, a library providing useful routines related to building, parsing, and iterating BSON documents.
Security Fix(es):
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.(CVE-2026-6691)
- Record
OESA-2026-2692- CVSS 4.0
- 8.6 High
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/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 - Updated
- 2026-11-02
OSVOESA-2026-2693
mongo-c-driver security update
mongo-c-driver is a project that includes two libraries: libmongoc, a client library written in C for MongoDB. libbson, a library providing useful routines related to building, parsing, and iterating BSON documents.
Security Fix(es):
The bson_validate function may return early on specific inputs and incorrectly report success. This behavior could result in skipping validation for BSON data, allowing malformed or invalid UTF-8 sequences to bypass validation and be processed incorrectly. The issue may affect applications that rely on these functions to validate untrusted BSON data before further processing. This issue affects MongoDB C Driver versions prior to 1.30.5, MongoDB C Driver version 2.0.0 and MongoDB C Driver version 2.0.1.(CVE-2026-6231)
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.(CVE-2026-6691)
- Record
OESA-2026-2693- CVSS 4.0
- 8.6 High
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/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 - Updated
- 2026-11-02
OSVUBUNTU-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.
- Record
UBUNTU-CVE-2026-6691- CVSS 4.0
- 8.6 High
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 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
mongo-c-driverDebian:12 |
before 1.23.1-1+deb12u3, plus listed versions 1.23.1-11.23.1-1+deb12u11.23.1-1+deb12u2 |
1.23.1-1+deb12u3 |
mongo-c-driverDebian:13 |
before 1.30.4-1+deb13u2, plus listed versions 1.30.4-11.30.4-1+deb13u1 |
1.30.4-1+deb13u2 |
mongo-c-driverDebian:14 |
before 2.2.0-1, plus listed versions 1.30.4-12.0.2-12.1.0-12.1.1-12.1.2-1 |
2.2.0-1 |
mongo-c-driveropenEuler:22.03-LTS-SP4 |
before 1.30.6-3.oe2203sp4 | 1.30.6-3.oe2203sp4 |
mongo-c-driveropenEuler:24.03-LTS-SP1 |
before 1.30.6-3.oe2403sp1 | 1.30.6-3.oe2403sp1 |
mongo-c-driveropenEuler:24.03-LTS-SP3 |
before 1.30.6-3.oe2403sp3 | 1.30.6-3.oe2403sp3 |
mongo-c-driveropenEuler:20.03-LTS-SP4 From an advisory covering 2 CVEs |
before 1.27.4-3.oe2003sp4 | 1.27.4-3.oe2003sp4 |
mongo-c-driverUbuntu:Pro:20.04:LTS |
All versions, plus listed versions 1.15.0-11.15.1-11.15.2-11.16.0-11.16.1-11.16.1-1build11.16.1-1build21.16.1-1ubuntu0.1~esm1 |
None known |
mongo-c-driverUbuntu:Pro:22.04:LTS |
All versions, plus listed versions 1.18.0-11.19.1-11.19.2-11.20.0-11.20.0-1build1 Show 4 moreShow less1.20.1-11.21.0-11.21.0-1build11.21.0-1ubuntu0.1~esm1 |
None known |
mongo-c-driverUbuntu:Pro:24.04:LTS |
All versions, plus listed versions 1.24.3-11.24.4-11.25.1-11.25.2-11.25.4-1 Show 4 moreShow less1.26.0-11.26.0-1.1ubuntu11.26.0-1.1ubuntu21.26.0-1.1ubuntu2+esm1 |
None known |
mongo-c-driverUbuntu:25.10 |
All versions, plus listed versions 1.30.2-11.30.4-1ubuntu1 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | ||
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-6691 is a high vulnerability (CVSS 8.6) in Mongodb C Driver, published May 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.13%, the 2nd percentile. Fixed in mongo-c-driver 1.23.1-1+deb12u3.
References
jira.mongodb.org/browse/CDRIVER-6134
nvd.nist.gov/vuln/detail/CVE-2026-6691
github.com/advisories/GHSA-587q-94wg-2pfp
security-tracker.debian.org/tracker/CVE-2026-6691
openeuler.org/zh/security/security-bulletins/detail?id=openEuler-SA-2026-2690
Show 8 moreShow less
ubuntu.com/security/CVE-2026-6691
cve.org/CVERecord?id=CVE-2026-6691