CVE-2026-33804

@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option

Published 16 Apr 2026Modified 17 Jun 2026CWE 436

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

GHSA7.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Trivy's own label is CRITICAL. Rated critical by NVD. Rated lower by GHSA (high).

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.

Affected packages and fixed versions

Source	Package	Fixed in
npm::GitHub Security Advisory npm	@fastify/middie	9.3.2

References

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