CVE-2026-92081
Published:September 16, 2026
Updated:September 22, 2026
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.
Affected Packages
fastify (CDN_JS):
Affected version(s) >=6.0.0-alpha.0 <6.0.0-alpha.4Fix Suggestion:
Update to version 6.0.0-alpha.4fastify (CDN_JS):
Affected version(s) >=5.0.0 <5.12.5Fix Suggestion:
Update to version 5.12.5https://github.com/fastify/fastify.git (GITHUB):
Affected version(s) >=v5.0.0 <v5.12.5Fix Suggestion:
Update to version v5.12.5fastify (NPM):
Affected version(s) >=6.0.0-alpha.0 <6.0.0-alpha.4Fix Suggestion:
Update to version 6.0.0-alpha.4fastify (NPM):
Affected version(s) >=5.0.0 <5.12.5Fix Suggestion:
Update to version 5.12.5Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.2
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.9
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Uncaught Exception
EPSS
Base Score:
0.40