CVE-2026-18691

EUVD-2026-56921

11.08.2026, 19:17

An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access to influence which authentication mechanism is used when one replica set member connects to another. Under certain conditions, this could cause the cluster's shared internal credential to be transmitted in a less-protected form, potentially allowing that credential to be recovered. If recovered, the credential could be used to authenticate as the internal superuser to nodes in the deployment.

Algorithm Downgrade

Provider	Type	Base Score	Atk. Vector	Atk. Complexity	Priv. Required	Vector
mongodb	CNA	8.8 HIGH	ADJACENT_NETWORK	LOW	NONE	CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Base Score

CVSS 3.x

EPSS Score

Percentile: Unknown

Early Detection

Affected products identified ahead of NVD analysis through intelligence sources.

Vendor	Product	Version	Source
mongodb	mongodb	8.3.0 ≤ 𝑥 < 8.3.8	CNA
mongodb	mongodb	8.0 ≤ 𝑥 < 8.0.29	CNA
mongodb	mongodb	7.0 ≤ 𝑥 < 7.0.40	CNA

Common Weakness Enumeration

CWE-757 - Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.

References

https://jira.mongodb.org/browse/SERVER-130264