MongoDB Server Intra-Cluster Auth Mechanism Manipulation (CVE-2026-18691)
CVE-2026-18691 Published on August 11, 2026
Improper Authentication in MongoDB Intra-Cluster Connections Allows Credential Exposure
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.
Vulnerability Analysis
Weakness Type
What is an Algorithm Downgrade Vulnerability?
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. When a security mechanism can be forced to downgrade to use a less secure algorithm, this can make it easier for attackers to compromise the software by exploiting weaker algorithm. The victim might not be aware that the less secure algorithm is being used. For example, if an attacker can force a communications channel to use cleartext instead of strongly-encrypted data, then the attacker could read the channel by sniffing, instead of going through extra effort of trying to decrypt the data using brute force techniques.
CVE-2026-18691 has been classified to as an Algorithm Downgrade vulnerability or weakness.
Products Associated with CVE-2026-18691
Want to know whenever a new CVE is published for MongoDB? stack.watch will email you.
Affected Versions
MongoDB Server:- Version 8.3.0 and below 8.3.8 is affected.
- Version 8.0 and below 8.0.29 is affected.
- Version 7.0 and below 7.0.40 is affected.