CVE-2026-19481: @fastify/busboy is a multipart form-data parser

Q: How do I fix CVE-2026-19481?

fastify\/busyboy: upgrade to 3.2.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-19481 being exploited?

CVE-2026-19481 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-19481 affect?

CVE-2026-19481 affects fastify\/busyboy. Severity is high (CVSS 7.5). @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

Q: How urgent is CVE-2026-19481?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-19481 is a high-severity flaw (CVSS 7.5) affecting fastify\/busyboy. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

@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 TypeErr

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 58%)
CISA exploited list	No
Weakness	CWE-754
Published	2026-08-13
Last modified	2026-09-03

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-09-03 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-13 09:17 UTCPublished CVE record published
2026-09-03 19:16 UTCUpdated Record last modified

fastify fastify\/busyboy UPGRADE

Affected: >= 1.0.0 and < 3.2.1

Fixed in: 3.2.1

Safe to downgrade to: a release before 1.0.0

1. Check installed version

npm ls fastifybusyboy

2. UPGRADE to 3.2.1

npm install fastifybusyboy@">=3.2.1"

3. If no update is available yet, DOWNGRADE to a release before 1.0.0

npm view fastifybusyboy versions npm install fastifybusyboy@"<1.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-19481?

fastify\/busyboy: upgrade to 3.2.1. Exact commands for each OS are on this page.

Is CVE-2026-19481 being exploited?

CVE-2026-19481 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-19481 affect?

CVE-2026-19481 affects fastify\/busyboy. Severity is high (CVSS 7.5). @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

How urgent is CVE-2026-19481?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-74866 MEDIUM 5.8 UPGRADE @fastify/busboy is a multipart form-data parser for Node.js
CVE-2026-19484 HIGH 7.5 UPGRADE @fastify/busboy is a multipart form-data parser

References

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