# CVE-2018-20802: Post-auth queries on compound index may crash mongod

> An authenticated user can crash the MongoDB server by sending specially crafted queries involving compound indexes.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Nov 2020
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-g6mr-mvf4-4wvj, UBUNTU-CVE-2018-20802

## What is CVE-2018-20802?

CVE-2018-20802 is a medium-severity denial of service vulnerability in Mongodb Mongodb, published on 23 Nov 2020. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A user authorized to perform database queries may trigger denial of service by issuing specially crafted queries with compound indexes affecting QueryPlanner. This issue affects MongoDB Server v3.6 versions prior to 3.6.9 and MongoDB Server v4.0 versions prior to 4.0.3.

Weakness: CWE-394 (Unexpected Status Code or Return Value)

## Which versions are affected by CVE-2018-20802?

It affects 1 product.


Products: Mongodb Mongodb.

## How do I fix CVE-2018-20802?

Upgrade to a fixed version.

## Is CVE-2018-20802 being exploited?

There is no known exploitation of CVE-2018-20802 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-2026-18691](https://insights.sbomify.com/CVE-2026-18691/): Improper Authentication in MongoDB Intra-Cluster Connections Allows Credential Exposure (critical 9.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-20802 and fix it if it is affected.

What it is: CVE-2018-20802 is a medium-severity denial of service vulnerability in Mongodb Mongodb, published on 23 Nov 2020. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-20802 in the wild and no public exploit code.

Affected product: Mongodb Mongodb. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2018-20802/ (Markdown: https://insights.sbomify.com/CVE-2018-20802/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20802
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20802
- OSV: https://osv.dev/vulnerability/CVE-2018-20802

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20802/
Summaries are generated and may contain mistakes; the official description above is the record.