---
id: CVE-2026-19484
aliases:
  - GHSA-xjh9-v7x6-24jw
title: >-
  @fastify/busboy vulnerable to Denial of Service via oversized multipart
  boundary
summary: >-
  @fastify/busboy vulnerable to Denial of Service via oversized multipart
  boundary
severity: high
cvss: 7.5
cwe:
  - CWE-835
  - CWE-1322
vendor: fastify
product: '@fastify/busboy'
ecosystem: npm
affected:
  - '@fastify/busboy >= 3.1.0, < 3.2.1'
patched:
  - '@fastify/busboy 3.2.1'
published: '2026-10-02'
updated: '2026-10-02'
sourceUpdated: '2026-10-02T23:17:29Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-xjh9-v7x6-24jw'
references:
  - url: 'https://github.com/fastify/busboy/security/advisories/GHSA-xjh9-v7x6-24jw'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19484'
  - url: >-
      https://github.com/fastify/busboy/commit/632a237e7fb6b3b7a30e0de8fab2ee72ca5bf722
  - url: 'https://cna.openjsf.org/security-advisories.html'
  - url: 'https://github.com/fastify/busboy/releases/tag/v3.2.1'
  - url: 'https://github.com/advisories/GHSA-xjh9-v7x6-24jw'
tags:
  - ghsa
  - npm
epss: 0.00615
epssPercentile: 0.47573
ingestedAt: '2026-10-02T23:34:57.390Z'
---

## Overview

### Impact

Versions of `@fastify/busboy` from 3.1.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The vendored streaming multipart search stores its default skip distance in a `Uint8Array(256)`. A multipart boundary of exactly 252 bytes makes the search needle 256 bytes, and the table entry wraps to zero, so a crafted request keeps the search in a CPU-bound loop and stalls the Node.js event loop. An unauthenticated client can trigger this with a single small request. Applications that use `@fastify/busboy` to parse multipart/form-data, directly or through `@fastify/multipart`, are affected.

### Patches

Fixed in version 3.2.1.

### Workarounds

Validate the multipart boundary before parsing and reject any boundary longer than the RFC 2046 limit of 70 characters (for example at a reverse proxy or in an onRequest hook). Upgrading to 3.2.1 removes the issue.

## Affected packages

- `@fastify/busboy >= 3.1.0, < 3.2.1`

## Remediation

Upgrade to a patched release:

- `@fastify/busboy 3.2.1`