CVE-2026-117531

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CVE-2026-117531

Summary: @fastify/multipart vulnerable to Denial of Service via a malformed upload hanging delayed file consumers

Details: @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.

References: https://cna.openjsf.org/security-advisories.html, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/117xxx/CVE-2026-117531.json, https://github.com/fastify/fastify-multipart/security/advisories/GHSA-5849-5m6q-9632, https://nvd.nist.gov/vuln/detail/CVE-2026-117531