CyberSecBulletin
CVE-2026-18691NVD status: Analyzed

MongoDB Server: Selection of Less-Secure Algorithm During Negotiation

Published Updated By the CyberSecBulletin desk

CVE-2026-18691 is a high-severity selection of less-secure algorithm during negotiation vulnerability in MongoDB Server from MongoDB, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. The record lists versions 8.3.8, 8.0.29, 7.0.40 as the first without the flaw, so updating MongoDB Server to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.36% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update MongoDB Server to 8.3.8 or 8.0.29 or 7.0.40, whichever matches your release line, or a later version.
  2. Update Mongodb to 7.0.40 or 8.0.29 or 8.3.8, whichever matches your release line, or a later version.
  3. Read the advisory on jira.mongodb.org for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
MongoDBMongoDB Server8.3.0 up to, but not including, 8.3.8; 8.0 up to, but not including, 8.0.29; 7.0 up to, but not including, 7.0.408.3.8, 8.0.29, 7.0.40
MongoDBMongodb7.0.0 up to, but not including, 7.0.40; 8.0.0 up to, but not including, 8.0.29; 8.2.0 through 8.2.12; 8.3.0 up to, but not including, 8.3.8; 9.0.0; 9.1.07.0.40, 8.0.29, 8.3.8

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
AdjacentThe attacker must be on the same local network segment.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (mongodb.com).

Scoring systemScoreSeverityScored by
CVSS 4.09.0CriticalCNA (mongodb.com)
CVSS 3.18.8HighCNA (mongodb.com)

Official description

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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Selection of Less-Secure Algorithm During Negotiation

A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used in a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.

More Selection of Less-Secure Algorithm During Negotiation vulnerabilities (CWE-757)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in MongoDB Server

All MongoDB Server vulnerabilities

Recent Selection of Less-Secure Algorithm During Negotiation vulnerabilities

Spotted an error? Tell us.