---
id: CVE-2026-117531
title: >-
  @fastify/multipart vulnerable to Denial of Service via a malformed upload
  hanging delayed file consumers
summary: >-
  @fastify/multipart is the multipart form-data and file upload plugin for the
  Fastify web framework. In versions 5.3.0 through 10.1.6, the plugin does not
  propagate a parser error to the file stream when a request body ends inside a
  file …
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-400
vendor: '@fastify/multipart'
product: '@fastify/multipart'
affected:
  - '@fastify/multipart >= 5.3.0 < 10.1.7'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-02T16:58:29.940282Z'
published: '2026-11-02'
updated: '2026-11-02'
sourceUpdated: '2026-11-02T16:58:46.632Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-117531'
references:
  - url: >-
      https://github.com/fastify/fastify-multipart/security/advisories/GHSA-5849-5m6q-9632
  - url: 'https://cna.openjsf.org/security-advisories.html'
tags:
  - cve.org
epss: 0.00329
epssPercentile: 0.2616
ingestedAt: '2026-11-05T19:30:42.715Z'
---

## Overview

@fastify/multipart is the multipart form-data and file upload plugin for the Fastify web framework. In versions 5.3.0 through 10.1.6, the plugin does not propagate a parser error to the file stream when a request body ends inside a file part with no closing boundary, even though the Content-Length is complete, the client does not abort, and no file size limit is exceeded. The plugin destroys the in-progress file stream without an error, so a handler that iterates the request parts and performs asynchronous work before consuming the file attaches to a stream that never emits an error or end event, and the request never responds while the connection stays open. An unauthenticated remote client can repeat these malformed uploads against such a route to accumulate pending connections and exhaust server resources, so the impact is availability only and exploitation depends on the application using a delayed file consumer. The issue is fixed in @fastify/multipart 10.1.7, where the parser error is propagated to the file stream so a delayed consumer settles with an error instead of hanging, and users should upgrade to 10.1.7 or later. There is no workaround other than upgrading.

## Affected

- `@fastify/multipart >= 5.3.0 < 10.1.7`

## Remediation

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