CVE-2026-33808

Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled. This allows complete bypass of path-scoped authentication middleware via duplicate slashes when ignoreDuplicateSlashes is enabled, or via semicolon delimiters when useSemicolonDelimiter is enabled. In both cases, Fastify router normalizes the URL and matches the route, but @fastify/express passes the original un-normalized URL to Express middleware, which fails to match and is skipped. An unauthenticated attacker can access protected routes by manipulating the URL path. PatchesUpgrade to @fastify/express v4.0.5 or later.

The following products are affected by CVE-2026-33808 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-33808.

URL	Resource
https://cna.openjsf.org/security-advisories.html
https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88