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.
CVSS Metrics
- Vector
- CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- Attack Vector
- network
- Complexity
- high
- Privileges
- none
- User Action
- none
- Scope
- unchanged
- Confidentiality
- high
- Integrity
- high
- Availability
- none
- Weaknesses
- CWE-436
Metadata
- Primary Vendor
- UNKNOWN
- Published
- 4/16/2026
- Last Modified
- 4/17/2026
- Source
- NIST NVD
- Note: Verify all details with official vendor sources before applying patches.
Affected Products
No affected products information available.
AI-Powered Remediation
Generate remediation guidance or a C-suite brief for this vulnerability.