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critical advisory

@fastify/express Authentication Bypass via URL Normalization Gaps

A vulnerability exists in `@fastify/express` v4.0.4 that allows complete bypass of path-scoped authentication middleware via URL normalization gaps, specifically through duplicate slashes and semicolon delimiters, leading to unauthorized access to protected routes.

@fastify/express fastify express authentication-bypass url-normalization cve-2026-33808
2r 1t 1c
critical advisory

Fastify/Express Middleware Path Doubling Authentication Bypass

A path handling bug in `@fastify/express` v4.0.4 `onRegister` function causes middleware paths to be doubled when inherited by child plugins, resulting in complete bypass of Express middleware security controls for all routes defined within child plugin scopes that share a prefix with parent-scoped middleware.

@fastify/express fastify express authentication-bypass middleware path-traversal
2r 1t