EUVD-2026-57757Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable endpoint, no credentials or interaction needed, crash-only impact with no data exposure or integrity loss.
Primary rating from Vendor (openjs).
CVSS VectorVendor: openjs
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
3DescriptionCVE.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
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. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The target application must accept multipart/form-data input (e.g., file upload or multi-field form endpoints) and process it through @fastify/busboy version 1.0.0-3.2.0. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H scores 7.5 and is fully consistent with the vulnerability description: network-reachable, no credentials required, low complexity, full availability impact on the vulnerable component. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker sends an HTTP POST request with Content-Type: multipart/form-data to any endpoint backed by @fastify/busboy, including a part header such as Content-Disposition: form-data; name="__proto__". The parser resolves __proto__ to the inherited Object.prototype reference, then attempts to call .push() on it as if it were an array; a TypeError is thrown synchronously, and if the application uses direct write or end integration, the uncaught exception terminates the Node.js worker process, taking the entire service offline. |
| Remediation | Vendor-released patch: @fastify/busboy 3.2.1. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, audit all deployed Fastify applications to identify which are using @fastify/busboy versions 1.0.0-3.2.0 and expose multipart upload endpoints; for affected systems, immediately implement input validation to reject multipart form headers containing prototype-pollution keywords (__proto__, constructor, prototype). …
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