CVE-2026-33808Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled.
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 9.1 CRITICAL (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-436
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Jun 17, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
fastify fastify/express fastify:fastify/express | before 4.0.5 | NVD |
References
- https://cna.openjsf.org/security-advisories.htmlvendor-advisory
- https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88exploit, mitigation, vendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.