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

Quick assessment

Affected
@fastify/busboy @fastify/busboy
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Fastify busboy是Fastify组织的一款处理Web表单数据的中间件。 Fastify busboy 1.0.0版本至3.2.0版本存在异常处理不当漏洞，该漏洞源于内部头解析器将头存储在普通JavaScript对象中且未正确处理原型继承属性名，攻击者可通过提交特制multipart form-data触发TypeError，导致未经身份验证的拒绝服务。

CVSS 7.5 · High EPSS 0.49% · P40

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
@fastify/busboy @fastify/busboy 1.0.0< 3.2.1 affected
3.2.1 unaffected
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I. Basic Information for CVE-2026-19481

Vulnerability Information
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Vulnerability Title
@fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
对因果或异常条件的不恰当检查
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify busboy 异常处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Fastify busboy是Fastify组织的一款处理Web表单数据的中间件。 Fastify busboy 1.0.0版本至3.2.0版本存在异常处理不当漏洞，该漏洞源于内部头解析器将头存储在普通JavaScript对象中且未正确处理原型继承属性名，攻击者可通过提交特制multipart form-data触发TypeError，导致未经身份验证的拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
@fastify/busboy @fastify/busboy 1.0.0 ~ 3.2.1 -

II. Public POCs for CVE-2026-19481

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 10398 chars
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III. Intelligence Information for CVE-2026-19481

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Vendor Advisories for CVE-2026-19481 (1)

IV. Related Vulnerabilities

Same product: @fastify/busboy
Same vendor: @fastify/busboy
Same weakness: CWE-754

V. Comments for CVE-2026-19481

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