PT-2026-33323 · @Fastify/Middie · @Fastify/Middie

Climba03003 + 3 · Published 2026-04-16 · Updated 2026-04-16 · CVE-2026-33804

Mitre

CVSS v3.1

7.4

High

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

@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.

Fix

Weakness Enumeration

CWE-436

Related Identifiers

CVE-2026-33804

Affected Products

@Fastify/Middie

References · 3

• https://nvd.nist.gov/vuln/detail/CVE-2026-33804 · Security Note
• https://cna.openjsf.org/security-advisories.html · Note
• https://github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6 · Note