# CVE-2026-19484: @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary

> Remote attackers can cause denial of service by sending crafted multipart requests that stall the Node.js event loop in the @fastify/busboy library.

- **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-xjh9-v7x6-24jw, MINI-2hp9-5x3q-wm7h, ROOT-APP-NPM-CVE-2026-19484

## What is CVE-2026-19484?

CVE-2026-19484 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 3.1.0 through 3.2.0, a remote unauthenticated attacker can stall the Node.js event loop by sending a multipart request whose boundary is crafted to a specific length. The vendored streaming search stores its skip table in a fixed 256 entry byte array, and a boundary of exactly 252 bytes makes the search needle 256 bytes, which truncates the default skip distance to zero and turns the search into a CPU bound loop on a small body. A single small request can keep one core busy and deny service to other requests handled by the same process. The issue is fixed in @fastify/busboy 3.2.1, which widens the skip table so the skip distance is preserved. Users should upgrade to 3.2.1.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-1322 (Use of Blocking Code in Single-threaded, Non-blocking Context)

## Which versions are affected by CVE-2026-19484?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@fastify/busboy` | npm | From 3.1.0 | 3.2.1 |
| `@fastify/busboy` | npm | From 3.1.0 | 3.2.1 |

Products: Fastify Fastify\/Busyboy.

## How do I fix CVE-2026-19484?

Upgrade @fastify/busboy to 3.2.1 or later.

## Is CVE-2026-19484 being exploited?

There is no known exploitation of CVE-2026-19484 in the wild and no public exploit code.

## Other vulnerabilities in @fastify/busboy

- [CVE-2026-19481](https://insights.sbomify.com/CVE-2026-19481/): @fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header (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-2026-19484 and fix it if it is affected.

What it is: CVE-2026-19484 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-2026-19484 in the wild and no public exploit code.

Affected packages and fixed versions:
- @fastify/busboy (npm): affected from 3.1.0; fixed in 3.2.1
- @fastify/busboy (npm): affected from 3.1.0; 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-2026-19484/ (Markdown: https://insights.sbomify.com/CVE-2026-19484/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19484
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19484
- OSV: https://osv.dev/vulnerability/CVE-2026-19484

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19484/
Summaries are generated and may contain mistakes; the official description above is the record.