CVE-2026-33808 (GCVE-0-2026-33808)

Vulnerability from cvelistv5 – Published: 2026-04-15 09:29 – Updated: 2026-04-15 13:10
VLAI?
Title
@fastify/express vulnerable to middleware authentication bypass via URL normalization gaps (duplicate slashes and semicolons)
Summary
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.
Severity ?
9.1 (Critical)
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
CWE
  • CWE-436 - Interpretation Conflict
Assigner
References
Impacted products
Vendor Product Version
fastify @fastify/express Affected: 0 , < 4.0.5 (semver)
Unaffected: 4.0.5 (semver)
Create a notification for this product.
Credits
FredKSchott mcollina UlisesGascon climba03003
Show details on NVD website
To clipboard 

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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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