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CVE PROGRAM SOURCE RECORD9.1 Critical

CVE-2026-33807

@fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes

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 products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

fastify @fastify/express

Default version status: unaffected

  • 0 to < 4.0.5affected
  • 4.0.5unaffected
pkg:npm/@fastify/express

References