CVE-2026-33808

@fastify/express has a middleware authentication bypass via URL normalization gaps (duplicate slashes and semicolons)

Published 15 Apr 2026Modified 26 Oct 2026CWE 436

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

GHSA9.1CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Trivy's own label is CRITICAL. Rated critical by NVD, GHSA.

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.

Affected packages and fixed versions

Source	Package	Fixed in
npm::GitHub Security Advisory npm	@fastify/express	4.0.5

References

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