CVE-2026-92081 fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses
An unauthenticated attacker can crash the server by sending HTTP/2 requests to routes using response trailers, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-92081?
CVE-2026-92081 is a medium-severity denial of service vulnerability in fastify, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-248
Which versions are affected by CVE-2026-92081?
2 open source packages ship an affected version, including fastify.
| Package | Affected | Fixed in |
|---|---|---|
fastify npm | All versions | 5.12.5 |
fastify npm | All versions | 5.12.5 |
How do I fix CVE-2026-92081?
Upgrade fastify to 5.12.5 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-92081 being exploited?
There is no known exploitation of CVE-2026-92081 in the wild and no public exploit code.
Sources
Also known as CLSA-2026-1791626840, CLSA-2026-1791667117, CLSA-2026-1791680737, CLSA-2026-1792233310, GHSA-4mh8-r7rc-xpvc, MINI-27p9-h6qr-8354.