CVE-2026-120215 @fastify/cors vulnerable to Denial of Service on a CORS preflight with the onSend hook
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-120215?
CVE-2026-120215 is a low-severity vulnerability in @fastify/cors, published on 2 Nov 2026.
Official description
@fastify/cors is the CORS plugin for the Fastify web framework. In versions 8.2.0 through 11.3.x, an application that registers the plugin with the non-default onSend hook option crashes on a CORS preflight. On an OPTIONS request that carries the Origin and Access-Control-Request-Method headers, the plugin calls reply.send from inside the onSend hook and re-enters the send pipeline, so a second write of the response headers throws an uncaught ERR_HTTP_HEADERS_SENT that can terminate the Node.js process when no process-level handler is installed. An unauthenticated remote client can trigger this with a single preflight request, so the impact is availability only, and exploitation requires the non-default onSend configuration. The issue is fixed in @fastify/cors 11.4.0, where onSend is no longer an accepted hook value and registration fails with a clear error instead of crashing at request time, and users should upgrade to 11.4.0 or later. As a workaround, use any other hook such as the default onRequest, or set preflight to false.
Weakness: CWE-248
Which versions are affected by CVE-2026-120215?
How do I fix CVE-2026-120215?
No fix has been published for CVE-2026-120215 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-120215 being exploited?
There is no known exploitation of CVE-2026-120215 in the wild and no public exploit code.
Sources
Also known as GHSA-8c3j-mm64-257c.