Vulnerability · Published Sep 16, 2026 · Assigned by openjs
CVE-2026-92081fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses
Medium 5.9
In plain English
A medium-severity security flaw in fastify from fastify. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
fastify is a fast and low-overhead web framework for Node.js. In versions before 5.12.5, when a route registers a response trailer via reply.trailer() and is served over HTTP/2, fastify unconditionally sets the Transfer-Encoding: chunked header, which is forbidden on HTTP/2, so Node.js throws while serializing the response headers. The exception is not caught and becomes an uncaughtException, so a single unauthenticated HTTP/2 request to any route that uses trailers crashes the server process and drops all in-flight requests, and it can be repeated on every restart. The issue is fixed in fastify 5.12.5, and users should upgrade to 5.12.5 or later. As a workaround, avoid registering response trailers with reply.trailer() on routes served over HTTP/2 until upgrading.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | fastify | 5.12.5 | GHSA-4mh8-r7rc-xpvc |
Affected products (as reported)
Weakness: CWE-248 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H