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.
Published: 2026-09-16
Score: 5.9 Medium
EPSS: < 1% Very Low
KEV: No
Impact: Denial of Service via server crash
Action: Immediate Patch
AI Analysis

Impact

A bug in fastify versions before 5.12.5 causes a node process to crash when a route registers a response trailer with reply.trailer() and the request is served over HTTP/2. The mishandled header results in Node.js throwing an uncaught exception that terminates the server process. A single unauthenticated HTTP/2 request to any affected route triggers the crash and aborts all in‑flight requests, effectively denying service until the process restarts.

Affected Systems

The affected product is the fastify web framework for Node.js. All releases prior to 5.12.5 are vulnerable. The fix is included in fastify 5.12.5 and later.

Risk and Exploitability

The vulnerability has a CVSS score of 5.9, indicating moderate severity, and the EPSS score is not available; it is not listed in the CISA KEV catalog. The attack vector is remote and unauthenticated: any client able to send an HTTP/2 request can trigger the crash. Because no authentication or privileged state is required, the exploit likelihood is high in environments that enable HTTP/2 and use the trailer feature.

Generated by OpenCVE AI on September 16, 2026 at 14:18 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade fastify to version 5.12.5 or later
  • Refactor or remove reply.trailer() usage on HTTP/2 routes until the upgrade is applied
  • Restart the server after applying the patch to ensure changes take effect

Generated by OpenCVE AI on September 16, 2026 at 14:18 UTC.

Tracking

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Advisories

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History

Wed, 16 Sep 2026 15:00:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify
Vendors & Products Fastify
Fastify fastify

Wed, 16 Sep 2026 14:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 16 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 threat_severity

Moderate

Wed, 16 Sep 2026 09:00:00 +0000

Type Values Removed Values Added
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.
Title fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses
Weaknesses CWE-248
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

Fastify Fastify
cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-09-16T14:00:59.305Z

Reserved: 2026-09-15T12:55:43.189Z

Link: CVE-2026-92081

cve-icon Vulnrichment

Updated: 2026-09-16T14:00:53.603Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-16T09:17:10.137

Modified: 2026-09-16T19:40:00.317

Link: CVE-2026-92081

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-16T08:52:49Z

Links: CVE-2026-92081 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-16T14:45:05Z

Weaknesses