---
id: CVE-2026-120216
title: >-
  fastify vulnerable to Denial of Service via uncaught exception on
  handlerTimeout with streaming responses
summary: >-
  fastify is a web framework for Node.js. In versions 5.8.0 through 5.12.7, when
  the server is configured with a nonzero handlerTimeout and a route returns a
  streaming response, a request whose stream has already sent its headers but
  stays…
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-248
vendor: fastify
product: fastify
affected:
  - fastify >= 5.8.0 < 5.12.8
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-02T16:55:59.970844Z'
published: '2026-11-02'
updated: '2026-11-02'
sourceUpdated: '2026-11-02T16:56:16.784Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-120216'
references:
  - url: 'https://github.com/fastify/fastify/security/advisories/GHSA-3qgw-9275-xf8w'
  - url: 'https://cna.openjsf.org/security-advisories.html'
tags:
  - cve.org
epss: 0.00329
epssPercentile: 0.2616
ingestedAt: '2026-11-05T19:30:42.714Z'
---

## Overview

fastify is a web framework for Node.js. In versions 5.8.0 through 5.12.7, when the server is configured with a nonzero handlerTimeout and a route returns a streaming response, a request whose stream has already sent its headers but stays open past the timeout crashes the server. When the timeout fires, Fastify tries to send a new error response on a response that has already started, raising an uncaught ERR_HTTP_HEADERS_SENT that terminates the Node.js process and interrupts any other in-flight requests. An unauthenticated remote client can trigger this with a single request to an affected streaming endpoint, so the impact is availability only, and exploitation requires the non-default handlerTimeout to be set. The default handlerTimeout of 0 is not affected. The issue is fixed in fastify 5.12.8, and users should upgrade to 5.12.8 or later. As a workaround, set handlerTimeout to 0, which disables the affected timeout path.

## Affected

- `fastify >= 5.8.0 < 5.12.8`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.