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9.1 Critical

CVE-2026-33808 Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify…

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 products and versions

Product Affected versions Fixed in
@fastify/express 4.0 earliest → < 4.0.5 4.0.5

References

Timeline

  1. Published
  2. Last modified

Other CVEs of @fastify/express

The 2 CVEs of @fastify/express →
CVE-2026-33807 @fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths… 9.1 Critical
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