CVE-2026-18549

HIGH CVSS 3.1: 7.5 EPSS 0.34%
Updated Sep 02, 2026
@Fastify/Multipart
Parameter Value
CVSS 7.5 (HIGH)
Affected Versions 5.3.0 — 10.1.1
Fixed In 10.1.1
Type CWE-400 (Uncontrolled Resource Consumption), CWE-664
Vendor @Fastify/Multipart
Public PoC No

@fastify/multipart is a multipart form-data parser for Fastify. In versions from 5.3.0 up to but not including 10.1.1, when the busboy fileSize limit truncates a file part, the plugin clears its internal current-file reference while the underlying stream is still open. If the client then aborts the connection before sending the terminating boundary, the abort cleanup finds no stream to destroy, so saveRequestFiles() never settles, the request handler hangs, and the temporary file already written to disk is never cleaned up.

An unauthenticated client can repeat this to permanently leak temporary files and suspended handler executions, leading to disk and event-loop exhaustion. The issue is fixed in @fastify/multipart 10.1.1. Users should upgrade to 10.1.1.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed

Impact Assessment

Confidentiality
None
No data leak
Integrity
None
No data modification
Availability
High
Complete denial of service

CVSS Vector v3.1

Vulnerable Products 1

Configuration From (including) Up to (excluding)
Fastify Fastify-Multipart
cpe:2.3:a:fastify:fastify-multipart:*:*:*:*:*:fastify:*:*
5.3.0 10.1.1