SCRAM Nonce Mismatch in libmongoc Lets MITM Capture Client Proof
CVE-2026-93394 Published on September 17, 2026
libmongoc SCRAM client nonce-validation bypass
A flaw in libmongoc's SCRAM authentication implementation caused the client to continue the authentication handshake and transmit the client proof even when a nonce mismatch was detected in the server's first message. An unauthorized party with a man-in-the-middle position could exploit this by injecting a crafted server-first-message containing a controlled salt and low iteration count, then capturing the resulting client proof to perform offline password cracking. This vulnerability is mitigated by TLS, which is standard in production deployments.
Vulnerability Analysis
CVE-2026-93394 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
Incorrect Implementation of Authentication Algorithm
The requirements for the software dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect. This incorrect implementation may allow authentication to be bypassed.
Products Associated with CVE-2026-93394
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Affected Versions
MongoDB Inc. C Driver:- Version 2.0.0 and below 2.3.2 is affected.