High severity7.4NVD Advisory· Published Apr 16, 2026· Updated May 14, 2026
CVE-2026-33804
CVE-2026-33804
Description
@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization performed by Fastify's router, allowing requests with duplicate slashes to bypass middleware authentication and authorization checks. This only affects applications using the deprecated ignoreDuplicateSlashes option. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds other than disabling the ignoreDuplicateSlashes option.
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Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
@fastify/middienpm | < 9.3.2 | 9.3.2 |
Affected products
2Patches
Vulnerability mechanics
References
4- cna.openjsf.org/security-advisories.htmlnvdVendor AdvisoryWEB
- github.com/advisories/GHSA-v9ww-2j6r-98q6ghsaADVISORY
- github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6nvdMitigationVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-33804ghsaADVISORY
News mentions
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