CVE-2026-33807

@fastify/express's middleware path doubling causes authentication bypass in child plugin scopes

Published 15 Apr 2026Modified 26 Oct 2026CWE 436

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

GHSA9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Trivy's own label is CRITICAL. Rated critical by GHSA.

Description

@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time, causing it to never match incoming requests. This results in complete bypass of Express middleware security controls, including authentication, authorization, and rate limiting, for all routes defined within affected child plugin scopes. No special configuration or request crafting is required. Upgrade to @fastify/express v4.0.5 or later.

Affected packages and fixed versions

Source	Package	Fixed in
npm::GitHub Security Advisory npm	@fastify/express	4.0.5

References

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