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@fastify/busboy CVE-2026-19481

| EUVDEUVD-2026-57757 HIGH
Improper Check for Unusual or Exceptional Conditions (CWE-754)
2026-08-13 openjs GHSA-x8mw-p69m-v3mx
Denial Of Service Node.js Fastify Busboy
7.5
CVSS 3.1 · Vendor: openjs
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Severity by source

Vendor (openjs) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
7.5 HIGH

Network-reachable endpoint, no credentials or interaction needed, crash-only impact with no data exposure or integrity loss.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
HIGH
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (openjs).

CVSS VectorVendor: openjs

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
Patch available
Aug 13, 2026 - 10:01 EUVD
Analysis Generated
Aug 13, 2026 - 09:31 vuln.today
CVE Published
Aug 13, 2026 - 08:31 cve.org
HIGH 7.5

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 18 npm packages depend on @fastify/busboy (7 direct, 11 indirect)

Ecosystem-wide dependent count for version 1.0.0.

DescriptionCVE.org

@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.

Articles & Coverage 2

News 7 New Node.js Vulnerabilities - 1 Critical, 6 High, 4 With POC Aug 14, 2026 News 3 New Node.js Vulnerabilities - 1 Critical, 2 High Severity Aug 13, 2026

AnalysisAI

Unauthenticated denial of service in @fastify/busboy versions 1.0.0 through 3.2.0 allows any network attacker to crash the Node.js process by submitting a multipart form with a header whose name collides with a prototype-inherited JavaScript property such as __proto__ or constructor. The internal header store uses a plain object inheriting from Object.prototype, so the inherited property resolves to a truthy non-array value that triggers a synchronous TypeError when array methods are invoked on it; in direct write/end usage paths this exception propagates uncaught and terminates the process. No public exploit code has been identified at time of analysis, but the attack is trivially constructable given the detailed advisory.

Technical ContextAI

The affected component is the multipart/form-data parsing library @fastify/busboy (CPE: cpe:2.3:a:@fastify/busboy:@fastify/busboy:*:*:*:*:*:*:*:*), the Fastify-maintained fork of the older busboy package, widely used in Node.js web applications to handle file uploads and form submissions. The root cause is classified as CWE-754 (Improper Check for Unusual or Exceptional Conditions): the internal header accumulation logic allocates a bare JavaScript object literal {} to store part headers by name. Because this object inherits from Object.prototype, property lookups for names like __proto__, constructor, or toString return truthy, non-array built-in values rather than undefined or an empty array. Downstream code assumes these slots contain arrays and calls array methods on them, triggering a TypeError. The behavior diverges by integration path: the pipe-based integration emits an error event that a well-written application could catch, but direct calls to write() or end() throw synchronously with no try/catch boundary, causing an unhandled exception that terminates the Node.js process. The fix in 3.2.1 creates the header object via Object.create(null), establishing a null prototype and eliminating inherited property interference.

RemediationAI

Vendor-released patch: @fastify/busboy 3.2.1. The fix is confirmed in the OpenJS Foundation security advisory at https://github.com/fastify/busboy/security/advisories/GHSA-x8mw-p69m-v3mx and referenced at https://cna.openjsf.org/security-advisories.html. Upgrade immediately by running npm install @fastify/busboy@3.2.1 or updating the version constraint in package.json. If upgrading is temporarily blocked, a compensating control is to add an application-level multipart size and header-count limit upstream of the parser (e.g., via a WAF or reverse proxy rule that rejects multipart requests containing headers with names matching __proto__, constructor, or other prototype keys). Be aware that this filter approach is brittle - encoding variants may bypass naive string matching - and it does not substitute for the patch. Another partial mitigation for direct write/end callers is to wrap the call in a try/catch and return an HTTP 400, preventing process termination at the cost of additional application-layer code; this does not apply to the pipe integration.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 12 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected

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CVE-2026-19481 vulnerability details – vuln.today
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