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.
Metrics
CVSS 3.1 9.1/10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| fastify | @fastify/express | < 4.0.5 |
References
- https://cna.openjsf.org/security-advisories.htmlVendor Advisory
- https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88Exploit, Mitigation, Vendor Advisory
- https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88Exploit, Mitigation, Vendor Advisory
Timeline
- Published
- Apr 15, 2026
- Last modified
- Oct 26, 2026
- NVD status
- Analyzed