Vulnerability · Published Aug 13, 2026 · Assigned by openjs
CVE-2026-19481@fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header
High 7.5
In plain English
A high-severity security flaw in @fastify/busboy from @fastify/busboy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
@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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | @fastify/busboy | 3.2.1 | GHSA-x8mw-p69m-v3mx |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| @fastify/busboy | @fastify/busboy | 1.0.0 – before 3.2.1 |
Weakness: CWE-754 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H