@fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header — GHSA-X8MW-P69M-V3MX

Summary

### Impact Versions of `@fastify/busboy` from 1.0.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The multipart header parser stores part-header names on a plain JavaScript object, so a part header named `__proto__` or `constructor` resolves to an inherited value that is not an array, and the parser throws `TypeError: this.header[h].push is not a function`. Through the documented `req.pipe(busboy)`…

Timeline

Published by source

2026-10-02

Risk context

• Reported severity or threat level: high.
• Reported CVSS score: 7.5 out of 10.
• Reported EPSS value: 0.00493.
• Review exposure for the affected product or family: npm: @fastify/busboy.

Product

npm: @fastify/busboy

What to do

General, cautious steps (verify details in the official source):

• Prioritize patching or mitigation immediately (treat as actively risky).
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-X8MW-P69M-V3MX

Source

GitHub

Vendor

GitHub

Published by source

2026-10-02

Last source activity

2026-10-02

Additional identifiers

CVE-2026-19481

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.