CVE-2026-18549
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk27th percentile - higher than 27% of all known CVEs
Summary
In @fastify/multipart, 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 aborts the connection before sending the terminating boundary, saveRequestFiles() never settles, and the temporary file 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 version 10.1.1.
Risk Assessment
The risk includes potential permanent disk exhaustion and suspension of request handling, leading to denial of service.
Recommendation
It is recommended to upgrade @fastify/multipart to version 10.1.1 or later.
Other vulnerabilities in @fastify/multipart
See all- CVE-2026-117531Medium
@fastify/multipart versions 5.3.0 through 10.1.6 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 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 doing asynchronous work before consuming the file attaches to a stream that never emits an error or end event, and the request never responds.
- CVE-2026-19474High
In @fastify/multipart, a multipart form-data parser for Fastify, versions from 3.0.0 up to but not including 10.1.1, request.saveRequestFiles() can leave completed temporary files on disk when a client disconnects during processing. An unauthenticated client can repeat this to cause persistent disk consumption and denial of service. The issue is fixed in version 10.1.1.
Original NVD description (English source)
@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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS