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TI-2026-15210 Aliases CVE-2026-18549

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

Priority MEDIUM 40CWE-400Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-400.

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00603 49th percentileScored 2026-11-07
Fix Fixed @fastify/multipart (@fastify/multipart): 10.1.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
@fastify/multipart@fastify/multipart5.3.0 to before 10.1.110.1.1Patch availableCNA
  • @fastify/multipart Vendor@fastify/multipart Affected 5.3.0 to before 10.1.1 Fixed in 10.1.1 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:fastify:fastify-multipart:*:*:*:*:*:fastify:*:*5.3.0 to before 10.1.1Vulnerablefastify
  • cpe:2.3:a:fastify:fastify-multipart:*:*:*:*:*:fastify:*:* Versions 5.3.0 to before 10.1.1 Vulnerable ·fastify

Remediation

  • Fix · CNA @fastify/multipart (@fastify/multipart) Fixed in 10.1.1

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    @fastify/multipart 10.1.1

    2 records Highest priority Priority MEDIUM 1 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2026-15859 @fastify/multipart vulnerable to Denial of Service via temporary file leak on aborted uploadPriority LOW 39
    Show all 2 records →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-18549

References

Advisory 2

  • TI-2026-83783 Denial of service in @fastify/multipart from malformed file uploads CVSS 3.1MEDIUM 5.9

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences