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Fencer Vulns
high 7.5

CVE-2026-18549 json

@fastify/multipart vulnerable to Denial of Service via aborted upload after fileSize limit

published 2026-08-15 2 mo ago modified 2026-09-02 2 mo ago also EUVD-2026-59759

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

@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.

Patch / fix

  • @fastify/multipart @fastify/multipart 10.1.1

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • @fastify/multipart @fastify/multipart

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-664 Improper Control of a Resource Through its Lifetime

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.