# CVE-2026-93394: MongoDB libmongoc SCRAM authentication nonce validation bypass

Source: https://junglewise.ai/threats/cve-2026-93394-mongodb-libmongoc-scram-authentication-nonce-validation-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-17. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93394 · Severity: low · CVSS 3.7 · Published 2026-09-17

libmongoc is the C driver used by MongoDB client applications to authenticate and communicate with MongoDB databases. A flaw in SCRAM authentication validation allows an attacker positioned between the client and server to inject a crafted authentication message, causing the client to proceed with authentication despite a nonce mismatch. An attacker could capture the resulting client proof and perform offline password cracking, though this risk is mitigated by TLS encryption commonly used in production.

Technologies: [MongoDB C Driver](https://junglewise.ai/threats/technologies/c-driver). Vendors: [MongoDB](https://junglewise.ai/threats/vendors/mongodb).

## Quick answers

**Is CVE-2026-93394 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93394 being exploited in the wild.

**How severe is CVE-2026-93394?** Low severity, with a CVSS score of 3.7, published 17 September 2026.

**Which products and versions are affected?** MongoDB libmongoc.

**Is there a fix for CVE-2026-93394?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-93394 attacked?** It is attacked over the network or from the adjacent network, in a software library.

**Am I affected by CVE-2026-93394?** Check whether you run MongoDB C Driver or MongoDB Libmongoc. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a nonce validation bypass in libmongoc's SCRAM (Salted Challenge Response Authentication Mechanism) implementation. The client fails to properly validate the server's nonce in the server-first-message during authentication handshake; when a mismatch is detected, the client continues the handshake and transmits the client proof instead of terminating the exchange. An attacker in a man-in-the-middle position can inject a crafted server-first-message with a controlled salt and low iteration count, then capture the resulting client proof for offline password cracking. The attack requires network access to the authentication channel and is mitigated in deployments using TLS, which protects the authentication exchange from tampering.

## Affected products

- MongoDB libmongoc

## Timeline

- 2026-09-17: disclosed

## References

- [https://jira.mongodb.org/browse/CDRIVER-6315](https://jira.mongodb.org/browse/CDRIVER-6315)

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