CVE-2026-19481: fastify fastify\/busyboy

Vulnerability summary

CVE-2026-19481 is a high (CVSS 7.5) vulnerability in fastify fastify\/busyboy. EPSS estimates a 0.49% chance of exploitation in the next 30 days, higher than 41.1% of scored vulnerabilities.

Timeline

1. 13-08-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-754Improper Check for Unusual or Exceptional ConditionsThe product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.