CVE-2026-33808

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.

PUBLISHED Reserved 2026-03-23 | Published 2026-04-15 | Updated 2026-04-15 | Assigner openjs

Problem types

CWE-436: Interpretation Conflict

Product status

Credits

FredKSchott reporter

mcollina remediation developer

UlisesGascon remediation reviewer

climba03003 remediation reviewer

References

github.com/...xpress/security/advisories/GHSA-6hw5-45gm-fj88 exploit

github.com/...xpress/security/advisories/GHSA-6hw5-45gm-fj88

cna.openjsf.org/security-advisories.html

cve.org (CVE-2026-33808)

nvd.nist.gov (CVE-2026-33808)

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