Fastify Middie Middleware Path Bypass_CVE-2026-22031

8.4 / 10

HIGH

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L

Description

@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.

Basic Information

ID CVE-2026-22031

Source GitHub_M

Published Jan 19, 2026 at 15:24

Affected Product

Vendor fastify

Product middie

Version < 9.1.0

Affected Versions fastify middie < 9.1.0

CWE Classification

CWE-177

References

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    "published": "2026-01-19T15:24:45.899Z",
    "modified": "2026-01-19T15:24:45.899Z",
    "type": "cve",
    "title": "Fastify Middie Middleware Path Bypass",
    "source": "GitHub_M",
    "references": "https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p\nhttps://github.com/fastify/middie/pull/245\nhttps://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effba\nhttps://github.com/fastify/middie/releases/tag/v9.1.0",
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