Description
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.
Published: 2026-09-17
Score: 6.3 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Thu, 17 Sep 2026 20:45:00 +0000

Type Values Removed Values Added
Description 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.
Title libmongoc SCRAM client nonce-validation bypass
Weaknesses CWE-303
References
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

cvssV4_0

{'score': 6.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: mongodb

Published:

Updated: 2026-09-17T20:31:27.875Z

Reserved: 2026-09-17T20:11:00.595Z

Link: CVE-2026-93394

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-17T21:17:56.307

Modified: 2026-09-17T21:17:56.307

Link: CVE-2026-93394

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses