Incomplete Cleanup Affecting @fastify/multipart package, versions <10.1.1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTIFYMULTIPART-18853842
- published16 Aug 2026
- disclosed15 Aug 2026
- creditiaohkut-from-NightWolf-Team
Introduced: 15 Aug 2026
NewCVE-2026-18549 (opens in a new tab)How to fix?
Upgrade @fastify/multipart to version 10.1.1 or higher.
Overview
@fastify/multipart is a Multipart plugin for Fastify
Affected versions of this package are vulnerable to Incomplete Cleanup due to the saveRequestFiles() multipart upload handling in index.js. An attacker can hang a request and leave temporary files behind by sending a file part that exceeds the fileSize limit and aborting before the multipart boundary is complete. When an application calls request.saveRequestFiles() on untrusted uploads, the request handler never settles and the temp file in os.tmpdir() is not removed. Repeating the request can exhaust disk space and worker or event-loop capacity, preventing normal file upload handling.
Workarounds
- Set
throwFileSizeLimit: falseto avoid thesaveRequestFiles()code path that drops the stream reference after afileSizetruncation, which prevents the hang and temp-file leak on aborted uploads.