# CVE-2026-19481: @fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header

> An attacker can crash the Node.js process by sending multipart headers with prototype names, causing denial of service in applications using this parser.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Aug 2026
- **Updated:** 13 Aug 2026
- **Also known as:** GHSA-x8mw-p69m-v3mx, MINI-vrm5-m8v6-vxxr, ROOT-APP-NPM-CVE-2026-19481

## What is CVE-2026-19481?

CVE-2026-19481 is a high-severity denial of service vulnerability in @fastify/busboy, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2026-19481?

2 open source packages ship an affected version, including @fastify/busboy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@fastify/busboy` | npm | From 1.0.0 | 3.2.1 |
| `@fastify/busboy` | npm | From 1.0.0 | 3.2.1 |

Products: Fastify Fastify\/Busyboy.

## How do I fix CVE-2026-19481?

Upgrade @fastify/busboy to 3.2.1 or later.

## Is CVE-2026-19481 being exploited?

There is no known exploitation of CVE-2026-19481 in the wild and no public exploit code.

## Other vulnerabilities in @fastify/busboy

- [CVE-2026-19484](https://insights.sbomify.com/CVE-2026-19484/): @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary (high 7.5)
- [CVE-2026-74866](https://insights.sbomify.com/CVE-2026-74866/): @fastify/busboy vulnerable to CRLF injection via multipart Content-Disposition filename and name (medium 5.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19481 and fix it if it is affected.

What it is: CVE-2026-19481 is a high-severity denial of service vulnerability in @fastify/busboy, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-19481 in the wild and no public exploit code.

Affected packages and fixed versions:
- @fastify/busboy (npm): affected from 1.0.0; fixed in 3.2.1
- @fastify/busboy (npm): affected from 1.0.0; fixed in 3.2.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-19481/ (Markdown: https://insights.sbomify.com/CVE-2026-19481/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19481
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19481
- OSV: https://osv.dev/vulnerability/CVE-2026-19481

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19481/
Summaries are generated and may contain mistakes; the official description above is the record.