CVE-2026-93394 libmongoc SCRAM client nonce-validation bypass
A man-in-the-middle attacker can bypass SCRAM nonce validation in the MongoDB C Driver to capture client proofs for offline password cracking.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-93394?
CVE-2026-93394 is a medium-severity vulnerability in MongoDB Inc. C Driver, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-303
Which versions are affected by CVE-2026-93394?
It affects 1 product.
Products include Mongodb C Driver.
How do I fix CVE-2026-93394?
Apply the vendor's patch.
Is CVE-2026-93394 being exploited?
There is no known exploitation of CVE-2026-93394 in the wild and no public exploit code.
Other vulnerabilities in MongoDB Inc. C Driver
- CVE-2026-93393 Heap overflow via oversized decrypted TLS record sequence in Windows Secure Channel stream
- CVE-2026-6691 MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
- 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()
Sources
Also known as DEBIAN-CVE-2026-93394, GHSA-cxv8-vf43-xcw5, UBUNTU-CVE-2026-93394.