CVE-2026-18691: MongoDB

High severity, CVSS 8.8. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• MongoDB MongoDB: from 7.0.0, before 7.0.40 (fixed in 7.0.40); from 8.0.0, before 8.0.29 (fixed in 8.0.29); from 8.2.0, up to and including 8.2.12; from 8.3.0, before 8.3.8 (fixed in 8.3.8); version 9.0.0 only; version 9.1.0 only

Published 2026-08-11. Last modified 2026-09-16.