@fastify/busboy vulnerable to Denial of Service via oversized multipart boundary

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-19484: 0.61% estimated exploitation activity in the next 30 days; percentile 49.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Versions of @fastify/busboy from 3.1.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The vendored streaming multipart search stores its default skip distance in a Uint8Array(256). A multipart boundary of exactly 252 bytes makes the search needle 256 bytes, and the table entry wraps to zero, so a crafted request keeps the search in a CPU-bound loop and stalls the Node.js event loop. An unauthenticated client can trigger this with a single small request. Applications that use @fastify/busboy to parse multipart/form-data, directly or through @fastify/multipart, are affected. Patches Fixed in version 3.2.1. Workarounds Validate the multipart boundary before parsing and reject any boundary longer than the RFC 2046 limit of 70 characters (for example at a reverse proxy or in an onRequest hook). Upgrading to 3.2.1 removes the issue.

Published by the source

2 Oct 2026, 23:16 UTC

Last modified by the source

2 Oct 2026, 23:30 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-xjh9-v7x6-24jw

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-xjh9-v7x6-24jw

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-xjh9-v7x6-24jw

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# Patch Next advisory brief: CVE-2026-19484

Advisory: @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary
IDs: CVE-2026-19484, GHSA-xjh9-v7x6-24jw
Record: https://patchnext.com/advisories/cve-2026-19484 (revision 3, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @fastify/busboy 3.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @fastify/busboy: affected >= 3.1.0, < 3.2.1; fixed in 3.2.1

## Suggested inspection (read-only)
- `npm ls @fastify/busboy --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @fastify/busboy.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xjh9-v7x6-24jw (GitHub-reviewed advisory GHSA-xjh9-v7x6-24jw lists affected ranges: npm @fastify/busboy >=3.1.0 <3.2.1)
- Verified: https://osv.dev/vulnerability/GHSA-xjh9-v7x6-24jw (OSV record GHSA-xjh9-v7x6-24jw lists affected ranges: npm @fastify/busboy >=3.1.0 <3.2.1 (fixed))

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