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CVE-2026-117531

MEDIUMCVSS 5.9/10

Last modified

CVE-2026-117531 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. @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.

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.

Metrics

CVSS 3.1
5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
@fastify/multipart@fastify/multipart>= 5.3.0, < 10.1.7

References

Timeline

Published
Last Modified
Status
Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-117531?
@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.
How severe is CVE-2026-117531?
CVE-2026-117531 has a CVSS score of 5.9/10 (MEDIUM severity).
How do I fix CVE-2026-117531?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST