CVE-2026-33804

HIGH

7.4

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.

CVE Details

CVSS v3.1 Score7.4

SeverityHIGH

CVSS VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack VectorNETWORK

ComplexityHIGH

Privileges RequiredNONE

User InteractionNONE

Published4/16/2026

Last Modified4/17/2026

Sourcenvd

Honeypot Sightings0

Weaknesses (CWE)

CWE-436

References

https://cna.openjsf.org/security-advisories.html(ce714d77-add3-4f53-aff5-83d477b104bb)

https://github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6(ce714d77-add3-4f53-aff5-83d477b104bb)

IOC Correlations

No correlations recorded

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