MongoDB C Driver GSSAPI Username Canonicalization Heap Overflow
CVE-2026-6691 Published on May 6, 2026
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.
Vulnerability Analysis
CVE-2026-6691 can be exploited with local system access, requires user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
What is a Classic Buffer Overflow Vulnerability?
The program copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. A buffer overflow condition exists when a program attempts to put more data in a buffer than it can hold, or when a program attempts to put data in a memory area outside of the boundaries of a buffer. The simplest type of error, and the most common cause of buffer overflows, is the "classic" case in which the program copies the buffer without restricting how much is copied. Other variants exist, but the existence of a classic overflow strongly suggests that the programmer is not considering even the most basic of security protections.
CVE-2026-6691 has been classified to as a Classic Buffer Overflow vulnerability or weakness.
Products Associated with CVE-2026-6691
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Affected Versions
MongoDB Inc. MongoDB C Driver:- Version 2.1.0, <= 2.1.2 is affected.