CVE-2026-19484 · GHSA-xjh9-v7x6-24jw

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

Risk score: 65/100
CVSS: 7.5 v3.1
Exploit chance (30 days): 0.6%
Published: 2 Oct 2026

Open in the live forecast Today's forecast

What to know

What it is: 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 re…
Affected: @fastify/busboy (npm) >= 3.1.0, < 3.2.1
Fix: Upgrade @fastify/busboy to 3.2.1 or later.
Exploitation: No known exploitation

Why it is Amber

CVSS 7.5 high
Remotely exploitable without logging in
On your watchlist: npm

Affected packages

Package	Ecosystem	Vulnerable	Fixed in
@fastify/busboy	npm	>= 3.1.0, < 3.2.1	3.2.1

References

Original description

### 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.

Last activity 2 Oct 2026. Patch Forecast updates every hour.