@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.
History

Thu, 16 Apr 2026 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Thu, 16 Apr 2026 14:45:00 +0000

Type Values Removed Values Added
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.
Title @fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option
Weaknesses CWE-436
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-04-16T14:41:48.659Z

Reserved: 2026-03-23T19:48:48.714Z

Link: CVE-2026-33804

cve-icon Vulnrichment

Updated: 2026-04-16T14:41:41.714Z

cve-icon NVD

Status : Received

Published: 2026-04-16T15:17:34.633

Modified: 2026-04-16T15:17:34.633

Link: CVE-2026-33804

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.