CVE-2026-120216

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CVE-2026-120216

Summary: fastify vulnerable to Denial of Service via uncaught exception on handlerTimeout with streaming responses

Details: fastify is a web framework for Node.js. In versions 5.8.0 through 5.12.7, when the server is configured with a nonzero handlerTimeout and a route returns a streaming response, a request whose stream has already sent its headers but stays open past the timeout crashes the server. When the timeout fires, Fastify tries to send a new error response on a response that has already started, raising an uncaught ERR_HTTP_HEADERS_SENT that terminates the Node.js process and interrupts any other in-flight requests. An unauthenticated remote client can trigger this with a single request to an affected streaming endpoint, so the impact is availability only, and exploitation requires the non-default handlerTimeout to be set. The default handlerTimeout of 0 is not affected. The issue is fixed in fastify 5.12.8, and users should upgrade to 5.12.8 or later. As a workaround, set handlerTimeout to 0, which disables the affected timeout path.

References: https://cna.openjsf.org/security-advisories.html, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/120xxx/CVE-2026-120216.json, https://github.com/fastify/fastify/security/advisories/GHSA-3qgw-9275-xf8w, https://nvd.nist.gov/vuln/detail/CVE-2026-120216