@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.

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History

Thu, 13 Aug 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 13 Aug 2026 11:00:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify busboy
Vendors & Products Fastify
Fastify busboy

Thu, 13 Aug 2026 09:00:00 +0000

Type Values Removed Values Added
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.
Title @fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header
Weaknesses CWE-754
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-08-13T14:25:29.262Z

Reserved: 2026-08-10T15:38:12.624Z

Link: CVE-2026-19481

cve-icon Vulnrichment

Updated: 2026-08-13T14:25:23.905Z

cve-icon NVD

Status : Received

Published: 2026-08-13T09:17:12.573

Modified: 2026-08-13T15:19:38.170

Link: CVE-2026-19481

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-13T11:00:12Z

Weaknesses