Vulnerability Description
@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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Fastify | Fastify-Multipart | >= 5.3.0, < 10.1.1 |
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.htmlThird Party Advisory
- https://github.com/fastify/fastify-multipart/security/advisories/GHSA-vmph-573x-MitigationVendor Advisory
FAQ
What is CVE-2026-18549?
CVE-2026-18549 is a vulnerability with a CVSS score of 7.5 (HIGH). @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 inter...
How severe is CVE-2026-18549?
CVE-2026-18549 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-18549?
Check the references section above for vendor advisories and patch information. Affected products include: Fastify Fastify-Multipart.