CVE-2026-92081: Fastify denial of service via unhandled exception on HTTP/2 trailer responses

CVE-2026-92081 · Severity: medium · CVSS 5.9 · Published 2026-09-16

Fastify is a popular web framework for Node.js used to build web applications and APIs. When HTTP/2 is enabled and a route uses response trailers, a single unauthenticated HTTP/2 request crashes the entire server process, dropping all active connections. An attacker can repeatedly trigger this to keep the service offline.

Technologies: fastify (npm). Vendors: npm.

Quick answers

Is CVE-2026-92081 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-92081 being exploited in the wild.
How severe is CVE-2026-92081?
Medium severity, with a CVSS score of 5.9, published 16 September 2026.
Which products and versions are affected?
fastify (npm) < 5.12.5, SEMVER:introduced=0,fixed=5.12.5.
Is there a fix for CVE-2026-92081?
Yes. fastify (npm): upgrade to 5.12.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-92081 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-92081?
Check whether you run fastify (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • fastify (npm): upgrade to 5.12.5 or later
    npm install fastify@5.12.5

Technical details

The vulnerability is an uncaught exception (CWE-248) in response header serialization. When a route registers a response trailer via reply.trailer() over HTTP/2, Fastify unconditionally sets the Transfer-Encoding: chunked header, which is forbidden by the HTTP/2 specification. Node.js throws an ERR_HTTP2_INVALID_CONNECTION_HEADERS exception during header serialization that is not caught, causing an uncaughtException that terminates the process. The attack requires no authentication or user interaction and is network-accessible; only HTTP/2-enabled Fastify servers with routes using trailers are affected (HTTP/1.x is unaffected). The fix is available in versions 5.12.5 and 4.29.2 and later.

Affected products

  • OpenJS Foundation Fastify before 5.12.5, before 4.29.2

Identifiers

  • CVE-2026-92081
  • GHSA-4mh8-r7rc-xpvc

Timeline

  • 2026-09-16: disclosed: CVE-2026-92081 and GHSA-4mh8-r7rc-xpvc published
  • 2026-09-16: patched: Fixed in versions 5.12.5 and 4.29.2

References

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