# CVE-2026-25224: Fastify denial of service via unbounded memory allocation in sendWebStream

Source: https://junglewise.ai/threats/cve-2026-25224-fastify-denial-of-service-via-unbounded-memory-allocation-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-02. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-25224 · Severity: low · CVSS 3.1 · Published 2026-02-02

Fastify is a popular Node.js web framework used to build REST APIs and web services. A denial-of-service vulnerability allows remote attackers to exhaust server memory by sending data slowly through Web Stream responses, causing application crashes or severe performance degradation. This impacts applications that stream data directly to clients without proper backpressure handling.

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

## Quick answers

**Is CVE-2026-25224 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-25224 being exploited in the wild.

**How severe is CVE-2026-25224?** Low severity, with a CVSS score of 3.1, published 2 February 2026.

**Which products and versions are affected?** fastify (npm) SEMVER:introduced=0,fixed=5.7.3.

**Is there a fix for CVE-2026-25224?** Yes. fastify (npm): upgrade to 5.7.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-25224 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-25224?** 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 5.7.3 or later

  ```sh
  npm install fastify@5.7.3
  ```


## Technical details

The vulnerability is a CWE-770 (Unbounded Resource Allocation) in Fastify's Web Streams response handling. When an application sends a ReadableStream or Response with a Web Stream body via reply.send(), a slow or non-reading client can trigger unbounded memory buffering because backpressure is not properly respected. The attack is network-based, requires no authentication or user interaction, but has high attack complexity. A successful exploit causes denial of service through process crash or server degradation. The issue is patched in Fastify 5.7.3 and later versions.

## Affected products

- Fastify Fastify <= 5.7.2

## Identifiers

- CVE-2026-25224
- GHSA-mrq3-vjjr-p77c

## Timeline

- 2026-02-02: disclosed
- 2026-02-02: patched: Fixed in version 5.7.3

## References

- [https://github.com/fastify/fastify/security/advisories/GHSA-mrq3-vjjr-p77c](https://github.com/fastify/fastify/security/advisories/GHSA-mrq3-vjjr-p77c)

## 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)