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

> An attacker with network access can force weaker authentication in MongoDB clusters to steal internal credentials and gain superuser access.

- **Severity:** Critical 9.0 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Aug 2026
- **Updated:** 11 Aug 2026
- **Also known as:** BIT-mongodb-2026-18691, GHSA-jx4v-jf9c-3rh7, MINI-9rvh-8jjx-56rv, MINI-hq2m-3h6f-vw76, MINI-jjf8-v5j5-pvjh, MINI-r99w-g6f3-wmph, UBUNTU-CVE-2026-18691

## What is CVE-2026-18691?

CVE-2026-18691 is a critical authentication bypass vulnerability in Mongodb Mongodb, published on 11 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### 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.

Weakness: CWE-757 (Selection of Less-Secure Algorithm During Negotiation)

## Which versions are affected by CVE-2026-18691?

1 open source package ship an affected version, including mongodb. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mongodb` | Bitnami | From 7.0.0 | 7.0.40, 8.0.29, 8.3.8, 9.0.2 |

Products: Mongodb Mongodb.

## How do I fix CVE-2026-18691?

Upgrade mongodb to a fixed version for your release line: 7.0.40, 8.0.29, 8.3.8 or 9.0.2.

## Is CVE-2026-18691 being exploited?

There is no known exploitation of CVE-2026-18691 in the wild and no public exploit code.

## Other vulnerabilities in Mongodb Mongodb

- [CVE-2025-14847](https://insights.sbomify.com/CVE-2025-14847/): MongoDB and MongoDB Server Improper Handling of Length Parameter Inconsistency (high 8.7, exploited in the wild)
- [CVE-2026-82067](https://insights.sbomify.com/CVE-2026-82067/): Auth bypass in MongoDB Server (critical 9.2)
- [CVE-2026-13072](https://insights.sbomify.com/CVE-2026-13072/): MongoDB Improper Input Validation in Compute Mode External Data Processing Leading to Memory Corruption (critical 9.2)
- [CVE-2017-15535](https://insights.sbomify.com/CVE-2017-15535/): Denial of service in n/a (critical 9.1)
- [CVE-2024-1351](https://insights.sbomify.com/CVE-2024-1351/): MongoDB Server may allow successful untrusted connection (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18691 and fix it if it is affected.

What it is: CVE-2026-18691 is a critical authentication bypass vulnerability in Mongodb Mongodb, published on 11 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18691 in the wild and no public exploit code.

Affected packages and fixed versions:
- mongodb (Bitnami): affected from 7.0.0; fixed in 7.0.40, 8.0.29, 8.3.8, 9.0.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18691/ (Markdown: https://insights.sbomify.com/CVE-2026-18691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18691
- OSV: https://osv.dev/vulnerability/CVE-2026-18691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18691/
Summaries are generated and may contain mistakes; the official description above is the record.