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Medium

fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses

  • Disclosed: 30.09.2026
  • Updated: 11.10.2026 10:22

Impact

fastify crashes with an uncaught ERR_HTTP2_INVALID_CONNECTION_HEADERS exception when a route that registers a response trailer via reply.trailer() is served over HTTP/2. Fastify unconditionally adds the Transfer-Encoding: chunked header when a trailer is set, which is forbidden on HTTP/2, so Node.js throws while serializing the response headers. The exception is not caught and becomes an uncaughtException, terminating the Node.js process.

One unauthenticated HTTP/2 request to any route that uses trailers is enough to crash the server, dropping all in-flight requests, and the request can be repeated to keep the process down. Applications are affected only when HTTP/2 is enabled (http2: true) and at least one route registers a trailer. HTTP/1.x responses are not affected.

Patches

Upgrade to fastify 5.12.5 or later.

Workarounds

Avoid registering response trailers with reply.trailer() on routes served over HTTP/2 until upgrading.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package fastify < 5.12.5 5.12.5

References

CVSS score 5.9/10
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-248
Platform
npm
Package
fastify
Disclosed
30.09.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-4mh8-r7rc-xpvc - CC BY 4.0

Vulnerability history: fastify

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (16) in the archive
Total entries
16
First → latest
07.2018 09.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 8
  • Medium 7
  • Low 1

Disclosures per year

Severity:
  1. fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses this entry
    Medium · 5.9 CVE-2026-92081 < 5.12.5 5.12.5
  2. fastify vulnerable to request body replacement via an async validation result collision
    High · 8.1 CVE-2026-84504 < 5.12.2 5.12.2
  3. fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers
    High · 7.5 CVE-2026-76169 >= 4.0.0, < 5.12.2 5.12.2
  4. fastify vulnerable to request validation bypass via skipped boolean false schemas
    High · 7.5 CVE-2026-84469 < 5.12.2 5.12.2
  5. fastify vulnerable to header validation bypass via incomplete schema case normalization
    High · 7.5 CVE-2026-84428 < 5.12.2 5.12.2
  6. Fastify's Content-Type header tab character allows body validation bypass
    High · 7.5 CVE-2026-25223 < 5.7.2 5.7.2
  7. Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass
    High · 7.5 CVE-2025-32442 >= 5.0.0, < 5.3.2, >= 4.29.0, < 4.29.1 5.3.2, 4.29.1
  8. fastify vulnerable to denial of service via malicious Content-Type
    High · 7.5 CVE-2022-39288 >= 4.0.0, < 4.8.1 4.8.1
  9. Denial of Service vulnerability with large JSON payloads in fastify
    High · 7.5 CVE-2018-3711 < 0.38.0 0.38.0

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