---
id: CVE-2026-18691
title: >-
  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
summary: >-
  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, t…
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-757
vendor: mongodb
product: mongodb
affected:
  - 'mongodb >= 7.0.0, < 7.0.40'
  - 'mongodb >= 8.0.0, < 8.0.29'
  - 'mongodb >= 8.2.0, <= 8.2.12'
  - 'mongodb >= 8.3.0, < 8.3.8'
  - mongodb = 9.0.0
  - mongodb = 9.1.0
patched:
  - mongodb 8.3.8
published: '2026-08-11'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T15:16:15.303'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-18691'
references:
  - url: 'https://jira.mongodb.org/browse/SERVER-130264'
    label: cna@mongodb.com
tags:
  - nvd
epss: 0.00355
epssPercentile: 0.26609
ingestedAt: '2026-08-29T19:41:15.522Z'
---

## Overview

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

- `mongodb >= 7.0.0, < 7.0.40`
- `mongodb >= 8.0.0, < 8.0.29`
- `mongodb >= 8.2.0, <= 8.2.12`
- `mongodb >= 8.3.0, < 8.3.8`
- `mongodb = 9.0.0`
- `mongodb = 9.1.0`

## Remediation

Upgrade past the affected range:

- `mongodb 8.3.8`