Is CVE-2026-19481 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-19481 being exploited in the wild.

How severe is CVE-2026-19481?

High severity, with a CVSS score of 7.5, published 2 October 2026.

Which products and versions are affected?

Fastify @Fastify/Busboy 1.0.0 to 3.2.0; @fastify/busboy (npm) >= 1.0.0, < 3.2.1, SEMVER:introduced=1.0.0,fixed=3.2.1.

How is CVE-2026-19481 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-19481?

Check whether you run Fastify @Fastify/Busboy or @fastify/busboy (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-19481: @fastify/busboy denial of service via prototype-named multipart header

Q: Is there a fix for CVE-2026-19481?

Yes. @fastify/busboy (npm): upgrade to 3.2.1 or later. Until then: Attach an error listener to the Busboy stream to handle parser failures, and wrap direct write()/end() calls in try/catch blocks to prevent process termination. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-19481 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-19481?

Check whether you run Fastify @Fastify/Busboy or @fastify/busboy (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-19481 · Severity: high · CVSS 7.5 · Published 2026-10-02

@fastify/busboy is a Node.js library that parses multipart form data uploads. An attacker can send a specially crafted form upload with a header field named `__proto__` or `constructor`, which causes the parser to crash with an unhandled error, terminating the application or triggering an error event. Any web application using this library is at risk, even without authentication.

Technologies: Fastify @Fastify/Busboy, @fastify/busboy (npm). Vendors: Fastify, npm.

Quick answers

Is CVE-2026-19481 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-19481 being exploited in the wild.
How severe is CVE-2026-19481?: High severity, with a CVSS score of 7.5, published 2 October 2026.
Which products and versions are affected?: Fastify @Fastify/Busboy 1.0.0 to 3.2.0; @fastify/busboy (npm) >= 1.0.0, < 3.2.1, SEMVER:introduced=1.0.0,fixed=3.2.1.
Is there a fix for CVE-2026-19481?: Yes. @fastify/busboy (npm): upgrade to 3.2.1 or later. Until then: Attach an error listener to the Busboy stream to handle parser failures, and wrap direct write()/end() calls in try/catch blocks to prevent process termination. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-19481 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-19481?: Check whether you run Fastify @Fastify/Busboy or @fastify/busboy (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

@fastify/busboy (npm): upgrade to 3.2.1 or later
```
npm install @fastify/busboy@3.2.1
```

Attach an error listener to the Busboy stream to handle parser failures, and wrap direct write()/end() calls in try/catch blocks to prevent process termination.

Technical details

The vulnerability is a prototype pollution issue in the multipart header parser: header names are stored directly on a plain JavaScript object, so reserved names like `__proto__` and `constructor` resolve to inherited values instead of arrays. When the parser attempts to push values onto these non-array fields, it throws a TypeError. This occurs before application middleware runs and can crash the process synchronously if error handling is not in place.

Affected products

Fastify @fastify/busboy 1.0.0 to 3.2.0

Identifiers

CVE-2026-19481
GHSA-x8mw-p69m-v3mx

Timeline

2026-08-12: disclosed
2026-08-12: patched: Version 3.2.1 released
2026-10-02: advisory

References

https://api.github.com/users/kq5y

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