CVE-2026-19481

What it is

@fastify/busboy is a multipart form-data parser. In versions 1.0.0 through 3.2.0, an attacker who can submit multipart form-data can crash the parser by sending a part header whose name is a prototype-inherited property such as __proto__ or constructor. The internal header parser stores headers in a plain JavaScript object and assumes each value is an array, so an inherited property name resolves to a truthy non-array value and triggers a TypeError. In the common pipe integration the failure surfaces as an error event, but in direct write or end usage the exception is thrown synchronously and can terminate the Node.js process, causing an unauthenticated denial of service. The issue is fixed in @fastify/busboy 3.2.1, which creates the header object with a null prototype. Users should upgrade to 3.2.1.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.5% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-13 09:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-03 19:16 UTC Last updatedMost recent change to the record

Details

Published

2026-08-13 09:17 UTC

Last modified

2026-09-03 19:16 UTC

Exploit probability

0.5% · EPSS, next 30 days

Weakness

CWE-754

Record status

Analyzed

Affected

• Fastify fastify\/busyboy < 3.2.1

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High