CVE-2026-22031
HIGH
GHSA-cxrg-g7r8-w69p
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
Lifecycle Timeline
3Description
@fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints. Version 9.1.0 fixes the issue.
Analysis
Middleware path-matching bypass in @fastify/middie before version 9.1.0 allows authenticated attackers to access protected endpoints by using URL-encoded characters in requests, as the middleware engine fails to decode paths while the underlying router does. An attacker with valid credentials can exploit this inconsistency to circumvent middleware security controls and access restricted functionality. …
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Remediation
Within 7 days: Identify all affected systems and apply vendor patches promptly. Monitor vendor channels for patch availability.
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External POC / Exploit Code
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