GitHub Advisoryadvisory · npm

GHSA-xjh9-v7x6-24jw @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary

HIGH Published 2026-10-02 Modified 2026-10-02 Official page ↗
Aliases
CVE-2026-19484
Ecosystem
npm
Packages
@fastify/busboy
Severity
High
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weaknesses
CWE-1322, CWE-835
Reviewed
2026-10-02

Affected packages

• npm @fastify/busboy: >= 3.1.0, < 3.2.1 → fixed in 3.2.1

Description

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.

Related

Alias · CVE (1)

  • CVE-2026-19484 @fastify/busboy is a multipart form-data parser. vulnerability

Weakness · CWE (2)

  • CWE-1322 Use of Blocking Code in Single-threaded, Non-blocking Context weakness
  • CWE-835 Loop with Unreachable Exit Condition weakness

References