CVE-2026-6691 MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
Heap buffer overflow in MongoDB C Driver's SASL integration allows code execution via crafted GSSAPI URIs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-6691?
CVE-2026-6691 is a high-severity memory corruption vulnerability in MongoDB C Driver, published on 6 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
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.
Which versions are affected by CVE-2026-6691?
It affects 1 product.
Products include Mongodb C Driver.
How do I fix CVE-2026-6691?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-6691 being exploited?
There is no known exploitation of CVE-2026-6691 in the wild and no public exploit code.
Other vulnerabilities in MongoDB C Driver
- CVE-2026-93393 Heap overflow via oversized decrypted TLS record sequence in Windows Secure Channel stream
- CVE-2026-84964 Heap corruption via OCSP request double free from crafted multi-URL certificate in TLS client
- CVE-2024-7553 Accessing Untrusted Directory May Allow Local Privilege Escalation
- CVE-2026-93395 Integer Underflow → Heap Out-of-Bounds Read in `bson_new_from_buffer()
- CVE-2025-12119 Bulk write with options may read invalid memory
Sources
Also known as DEBIAN-CVE-2026-6691, GHSA-587q-94wg-2pfp, OESA-2026-2690, OESA-2026-2691, OESA-2026-2692, UBUNTU-CVE-2026-6691.