# CVE-2026-117531: @fastify/multipart vulnerable to Denial of Service via a malformed upload hanging delayed file consumers

Status: published. Published: 2026-11-02. Updated: 2026-11-02.

@fastify/multipart is the multipart form-data and file upload plugin for the Fastify web framework. In versions 5.3.0 through 10.1.6, the plugin 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 the 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 that iterates the request parts and performs asynchronous work before consuming the file attaches to a stream that never emits an error or end event, and the request never responds while the connection stays open. An unauthenticated remote client can repeat these malformed uploads against such a route to accumulate pending connections and exhaust server resources, so the impact is availability only and exploitation depends on the application using a delayed file consumer. The issue is fixed in @fastify/multipart 10.1.7, where the parser error is propagated to the file stream so a delayed consumer settles with an error instead of hanging, and users should upgrade to 10.1.7 or later. There is no workaround other than upgrading.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- @fastify/multipart / @fastify/multipart (@fastify/multipart): ≥ 5.3.0; < 10.1.7 (affected, semver); 10.1.7 (unaffected, semver). Source: CNA: openjs

## Severity and prioritization

- CVSS 3.1: 5.9 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: openjs

- CVSS 3.1: 5.9 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: ce714d77-add3-4f53-aff5-83d477b104bb

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-400

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/fastify/fastify-multipart/security/advisories/GHSA-5849-5m6q-9632 (CNA: openjs)

- https://cna.openjsf.org/security-advisories.html (CNA: openjs)

- https://cna.openjsf.org/security-advisories.html (ce714d77-add3-4f53-aff5-83d477b104bb)

- https://github.com/fastify/fastify-multipart/security/advisories/GHSA-5849-5m6q-9632 (ce714d77-add3-4f53-aff5-83d477b104bb)

## Provenance

- CNA: openjs: https://www.cve.org/CVERecord?id=CVE-2026-117531; retrieved 2026-11-02; source updated 2026-11-02

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-117531; retrieved 2026-11-02; source updated 2026-11-02

Revision: 9f5e9f2a7cd20d8d2a6b84a29ef53f422dbb512ed9b20560bc85717c2b977a85

Canonical: https://y2.dev/cve/CVE-2026-117531