# CVE-2018-3711: Fastify denial of service with large JSON payloads

Source: https://junglewise.ai/threats/cve-2018-3711-fastify-denial-of-service-with-large-json-payloads  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2018-07-18. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2018-3711 · Severity: low · CVSS 3.1 · Published 2018-07-18

Fastify is a popular Node.js web framework used to build HTTP APIs and web services. A denial of service vulnerability allows attackers to crash or hang the server by sending requests with extremely large JSON payloads, disrupting service availability for legitimate users.

Technologies: [fastify (npm)](https://junglewise.ai/threats/technologies/fastify). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2018-3711 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2018-3711 being exploited in the wild.

**How severe is CVE-2018-3711?** Low severity, with a CVSS score of 3.1, published 18 July 2018.

**Which products and versions are affected?** fastify (npm) SEMVER:introduced=0,fixed=0.38.0.

**Is there a fix for CVE-2018-3711?** Yes. fastify (npm): upgrade to 0.38.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2018-3711 attacked?** It is attacked over the network.

**Am I affected by CVE-2018-3711?** Check whether you run fastify (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- fastify (npm): upgrade to 0.38.0 or later

  ```sh
  npm install fastify@0.38.0
  ```


## Technical details

Fastify versions before 0.38.0 are vulnerable to denial of service when processing HTTP requests with Content-Type set to application/json and exceptionally large payloads. The vulnerability stems from insufficient limits on request body size in the default JSON body parser, allowing attackers to exhaust server resources (memory and CPU) without authentication or user interaction. The attack vector is network-based and unauthenticated. Affected versions are all releases up to and including 0.37.0. The fix introduces a configurable jsonBodyLimit option to restrict the maximum size of JSON request bodies.

## Affected products

- Fastify Fastify <0.38.0

## Identifiers

- CVE-2018-3711
- GHSA-mq6c-fh97-4gwv

## Timeline

- 2018-06-07: disclosed: CVE-2018-3711 published on NVD
- 2018-01-08: patched: Fix merged in PR #627
- 2018-07-18: advisory: GHSA-mq6c-fh97-4gwv published

## References

- [https://github.com/fastify/fastify/pull/627](https://github.com/fastify/fastify/pull/627)

## Related threats

- [fastify is vulnerable to header validation bypass via case-sensitive propertyNames](https://junglewise.ai/threats/cve-2026-107832-fastify-is-a-fast-and-low-overhead-web-framework-for-node-js-in)
- [Fastify denial of service via unhandled exception on HTTP/2 trailer responses](https://junglewise.ai/threats/cve-2026-92081-fastify-denial-of-service-via-unhandled-exception-on-http-2)
- [Fastify header validation bypass via incomplete schema case normalization](https://junglewise.ai/threats/cve-2026-84428-fastify-header-validation-bypass-via-incomplete-schema-case)
- [Fastify request body replacement via async validation result collision](https://junglewise.ai/threats/cve-2026-84504-fastify-request-body-replacement-via-async-validation-result)
- [Fastify request validation bypass via skipped boolean false schemas](https://junglewise.ai/threats/cve-2026-84469-fastify-request-validation-bypass-via-skipped-boolean-false)