CVE-2026-22037
HIGH
GHSA-g6q3-96cp-5r5m
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
Lifecycle Timeline
3Tags
Description
The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 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. The vulnerability is caused by how @fastify/express matches requests against registered middleware paths. This vulnerability is similar to, but differs from, CVE-2026-22031 because this is a different npm module with its own code. Version 4.0.3 of @fastify/express contains a patch fort the issue.
Analysis
The @fastify/express plugin prior to version 4.0.3 allows authenticated attackers to bypass path-based middleware restrictions by submitting URL-encoded characters in requests, such as using /%61dmin instead of /admin. While the middleware engine fails to match the encoded path, the underlying Fastify router correctly decodes it and routes the request to handlers, enabling unauthorized access to protected endpoints. …
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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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