CVE-2026-33808
CVE-2026-33808 · @fastify/express vulnerable to middleware authentication bypass via URL normalization gaps (duplicate slashes and semicolons)
This page contains facts from public vulnerability sources. Check the original advisory before updating.
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.
CVSS 9.1 · Critical · EPSS 0.5% · Fix available
- Published
- Updated
Stack: node
Affected products and versions
@fastify/express
- Versions
- ≥ 0, < 4.0.5: Affected (semver)
- 4.0.5: Not affected (semver)
Update to 4.0.5
@fastify/express npm
- Affected ranges
- SEMVER: < 4.0.5
Update to 4.0.5