All vulnerabilities
CVE-2026-92081GHSA-4mh8-r7rc-xpvc

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

fastify fastifynpmFrameworks
Open in ThreatlineRecord JSON
CVSS
5.9Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.41%Chance of exploitation activity in the next 30 days, higher than 34% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in5.12.5Fixed versionGitHub
Published16 Sep 2026Updated 1 Oct 2026CVE List

What fixes it

  • 5.12.5fastify, npmGitHubnpm install fastify@5.12.5
  • 5.12.5fastifyCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

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.

Text from GitHub Advisory Database

Affected versions 4

  • fastify, npm< 5.12.5GitHub
  • fastifyaffected: all versions before 5.12.5CVE List
  • fastifyunaffected: 5.12.5CVE List
  • fastify, npmfrom first release, fixed in 5.12.5OSV

References 7