CVE-2026-117531
Received Received - Intake

Denial of Service in Fastify Multipart Plugin

Publication date: 2026-11-02

Last updated on: 2026-11-02

Assigner: openjs

Description
@fastify/multipart is the multipart form-data and file upload plugin for the Fastify web framework. In versions 5.3.0 through 10.1.6, the plugin does not propagate a parser error to the file stream when a request body ends inside a file part with no closing boundary, even though the Content-Length is complete, the client does not abort, and no file size limit is exceeded. The plugin destroys the in-progress file stream without an error, so a handler that iterates the request parts and performs asynchronous work before consuming the file attaches to a stream that never emits an error or end event, and the request never responds while the connection stays open. An unauthenticated remote client can repeat these malformed uploads against such a route to accumulate pending connections and exhaust server resources, so the impact is availability only and exploitation depends on the application using a delayed file consumer. The issue is fixed in @fastify/multipart 10.1.7, where the parser error is propagated to the file stream so a delayed consumer settles with an error instead of hanging, and users should upgrade to 10.1.7 or later. There is no workaround other than upgrading.

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Meta Information

Published
2026-11-02
Last Modified
2026-11-02
Generated
2026-11-02
AI Q&A
2026-11-02
EPSS Evaluated
N/A
NVD
CVE-2026-117531

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
@fastify/multipart @fastify/multipart 5.3.0

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.

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Executive Summary

This vulnerability affects the @fastify/multipart package, versions 5.3.0 through 10.1.6. When a malformed multipart upload request ends inside a file part without a proper closing boundary, the plugin fails to propagate a parser error to the file stream. This leaves asynchronous handlers waiting indefinitely for a stream that never emits an error or end event, causing requests to hang while connections remain open.

Detection Guidance

Monitor for hanging HTTP connections during file uploads. Check for slow or unresponsive requests in Fastify server logs. Use tools like netstat or ss to identify persistent connections from the same client IP.

Impact Analysis

An unauthenticated remote attacker can exploit this by sending repeated malformed upload requests. This accumulates pending connections and exhausts server resources, leading to a Denial of Service (DoS) where the server becomes unavailable due to resource exhaustion.

Compliance Impact

This vulnerability primarily impacts system availability by allowing unauthenticated remote clients to exhaust server resources through malformed file uploads. It does not directly affect data confidentiality or integrity, which are key concerns for GDPR and HIPAA. However, prolonged service unavailability could interfere with compliance requirements for timely data processing or access, depending on the application's role in handling regulated data.

Mitigation Strategies

Upgrade @fastify/multipart to version 10.1.7 or later immediately. If immediate upgrade is not possible, restrict file upload endpoints or implement rate limiting to reduce exposure.

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