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

Source: https://junglewise.ai/threats/cve-2026-92081-fastify-denial-of-service-via-unhandled-exception-on-http-2  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-16. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/fastify). Vendors: [npm](https://junglewise.ai/threats/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

  ```sh
  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

- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fastify/security/advisories/GHSA-4mh8-r7rc-xpvc](https://github.com/fastify/fastify/security/advisories/GHSA-4mh8-r7rc-xpvc)

## Related threats

- [fastify is vulnerable to header validation bypass via case-sensitive propertyNames](https://junglewise.ai/threats/cve-2026-107832-fastify-is-a-fast-and-low-overhead-web-framework-for-node-js-in)
- [Fastify header validation bypass via incomplete schema case normalization](https://junglewise.ai/threats/cve-2026-84428-fastify-header-validation-bypass-via-incomplete-schema-case)
- [Fastify request body replacement via async validation result collision](https://junglewise.ai/threats/cve-2026-84504-fastify-request-body-replacement-via-async-validation-result)
- [Fastify request validation bypass via skipped boolean false schemas](https://junglewise.ai/threats/cve-2026-84469-fastify-request-validation-bypass-via-skipped-boolean-false)
- [Fastify authentication bypass via malformed URLs in encapsulated handlers](https://junglewise.ai/threats/cve-2026-76169-fastify-authentication-bypass-via-malformed-urls-in-encapsulated)