Vulnerability · Published May 6, 2026 · Assigned by mongodb
CVE-2026-6691MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
High 7.8
In plain English
A high-severity buffer overflow in MongoDB C Driver from MongoDB Inc.. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 2% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)7.8High
Exploit odds (30 days)0.1%top 97.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mongo-c-driver | 1.23.1-1+deb12u3 | DEBIAN-CVE-2026-6691 |
| Debian:13 | mongo-c-driver | 1.30.4-1+deb13u2 | DEBIAN-CVE-2026-6691 |
| Debian:14 | mongo-c-driver | 2.2.0-1 | DEBIAN-CVE-2026-6691 |
| Ubuntu:25.10 | mongo-c-driver | no fix listed | UBUNTU-CVE-2026-6691 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MongoDB Inc. | MongoDB C Driver | 2.1.0 – through 2.1.2 |
Weakness: CWE-120 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H