Vulnerability Description
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.
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj
- https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj
FAQ
What is CVE-2026-33808?
CVE-2026-33808 is a documented vulnerability. 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-s...
How severe is CVE-2026-33808?
CVSS scoring is not yet available for CVE-2026-33808. Check NVD for updates.
Is there a patch for CVE-2026-33808?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.