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.
Scoring
- Severity
- CRITICAL
- CVSS base score
- 9.1
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- EPSS probability
- 0.48%
- CWE
- CWE-436
- Published
- 2026-04-15
- Last modified
- 2026-04-15
Affected products
- fastify @fastify/express
- fastify @fastify/express
Weakness type
Related vulnerabilities
- CVE-2026-87627 — Interpretation conflict in Safebrowsing in Google Chrome on on Mac prior to 153.0.8010.36 allowed a...
- CVE-2026-82537 — Roo-Code 3.54.0 Auto-Approve Bypass via Shell Parser Word-Boundary Mismatch
- CVE-2026-81378 — Visual Studio Code Security Feature Bypass Vulnerability
- CVE-2026-85184 — @fastify/middie vulnerable to path-scoped middleware bypass via absolute-form request target
- CVE-2026-84394 — fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
- CVE-2026-63435 — Mail: Email address spoofing via malformed RFC 2047 encoded-words
- CVE-2026-75931 — fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
- CVE-2026-57580 — authentik: Account Takeover via SAML NameID Comment Truncation